Before getting into that, I want to clear up some terminology. Common usage of the word masturbation is limited to an individual sexually pleasuring themselves, but the dictionary definition would also include a spouse manually stimulating their partner in foreplay. Because of this it is fairly common for church leaders to use the term 'self-abuse' rather than masturbation. Manual stimulation of one's partner in foreplay is not sinful.
Intent is also a a factor, as in any sin. If there is a medical purpose (for example, so a couple can conceive via IVF) then it is not sinful. For the purposes of this post I will use the word masturbation to refer to the act of deliberately stimulating one's own genitals to produce sexual pleasure, arousal and/or orgasm for the purpose of sexual self-gratification.
From past experience, I'm aware there are some members who are heavily vested in some of these myths, so I'm going to try and be as thorough as possible. If it seems like overkill please bear with it.
Myth 1: Avoiding masturbation is just counsel, not a commandment.
While it is true that there is not a specific condemnation of masturbation in scripture, our knowledge of God's commandments are not limited to that one source. In the October 1980 General Conference report is a speech by President Spencer W Kimball on morality. In it he says the following:
Masturbation, a rather common indiscretion, is not approved of the Lord nor of his church, regardless of what may have been said by others whose “norms” are lower. Latter-day Saints are urged to avoid this practice. Anyone fettered by this weakness should abandon the habit before he goes on a mission or receives the holy priesthood or goes in the temple for his blessings. (link)
Some have taken this quote and focused only on certain small parts, like 'common indiscretion' and use that to argue that it is not a sin and we are not commanded against it. This overlooks the fact that every sin is an indiscretion. It also ignores that further on this same speech he specifically lists masturbation as one of a number of reprehensible sexual sins.
In this quote a prophet of the Lord, acting in his office as Prophet and as President of the church, clearly lays out that both the Lord, and the Church do not approve of it. This is not mere policy or council. To deliberately rebel and do something the Lord has disapproved of is sin. President Kimball was the only one in that day who could legitimately speak on behalf of the Lord and on behalf of the Church and here he does so in no uncertain terms.
This is by far the clearest and most authoritative speech against masturbation we have in modern times, and that is also the reason why when this topic comes up in church publications this talk is nearly always quoted. I will be referring back to this again further down in this post as 'the Kimball quote'.
It is not the only such declaration by prophets and apostles either. In the October 1983 General Conference President Benson, and President of the Quorum of the Twelve Apostles refers to self-abuse as being one of several sins that are 'like unto' adultery (link). Elder Boyd K. Packer delivered a talk specifically about masturbation in the October 1976 Priesthood Session of General Conference, and that talk was turned into a pamphlet that was in print for 40 years.
Elder Vaughn J. Featherstone in the April 1975 General Conference said:
Now, my young friends, and I am sorry to say, many adults, how about all those of you who have a masturbation problem?... We don’t have to buckle under Satan’s temptations. That urge does not have to be satisfied. (link)
Apostle Rudger Clawson recorded in 1902 that "Pres. Joseph F. Smith called it [masturbation] 'a most damnable and pernicious practice'. And if you want to go way back, in 1870 First Counselor George A. Smith called the practice evil.
Myth 2: Masturbation is a violation of the Law of Chastity
Because masturbation is a sexual sin, and was soundly condemned, and was often listed alongside other sexual sins that were violations of the Law of Chastity, some members including Bishops and Stake Presidents came to assume that masturbation was a violation of the Law of Chastity itself.
This lead to some of those struggling to overcome it feeling far more anguish than what the situation called for, or for local leaders to deal with such cases in ways that were perhaps too harsh.
Not every sexual sin is a violation of the Law of Chastity. To break the Law of Chastity one must have a sexual relationship with somebody else who is not their lawful spouse. Masturbation is a solo act, so while it is a sexual sin, it is not a violation of the Law of Chasity.
As far as I can tell the church never stated that masturbation was a violation of the Law of Chastity or treated it like one when there were no other sins of a more serious nature involved.
Currently the Church Handbook of Instructions (Handbook 1, Section 6.7.1) lists it as something that normally does not need the Bishop to call for a Disciplinary Council. Other wrongs that fall into that category are not paying tithing, or not living the Word of Wisdom, or using pornography. Bishops are free to handle the situation through informal discipline such providing counsel and warnings, or prohibiting them from taking the sacrament, entering the temple, or exercising their priesthood. Adultery and fornication are listed as serious transgressions that normally do require a Disciplinary Council. This fits with what is stated in the Kimball quote, that a member should free themselves of this before going on a mission, entering the temple or advancing in the priesthood.
Myth 3: Masturbation is not a big deal
While it is not good to cast masturbation as a sin next to murder, it also is not good to minimize it as an excuse to continue doing it. While it is true that there are far more serious sins than masturbation, the fact remains that this is something that will affect your worthiness to enter the the temple and partake of the sacrament. That is serious enough that members should strive to avoid this and repent of it as necessary.
Myth 4:The church only tells singles and youth to not do it.
Many of the warnings against masturbation are directed at the Aaronic Priesthood or the Youth and YSA member of the church, but it is a mistake to think this only applies to them.
If you go back to the Conference Report where the Kimball quote comes from, you will see the talk's title and subtitle are "President Kimball Speaks Out on Morality - Special Message to All Latter-day Saints". The quote itself specifies "Anyone fettered by this weakness should abandon the habit..."
Page 219 of the Eternal Marriage Institute Manual (obviously for those preparing for marriage) quotes from President Kimball's talk where he condemns masturbation. Lesson 33 of the New Testament Gospel Doctrine manual (where most married members would be during Sunday School) contains this:
Elder Richard G. Scott of the Quorum of the Twelve taught: “Any sexual intimacy outside of the bonds of marriage—I mean any intentional contact with the sacred, private parts of another’s body, with or without clothing—is a sin and is forbidden by God. It is also a transgression to intentionally stimulate these emotions within your own body”(in ConferenceReport, Oct. 1994, 51; or Ensign, Nov. 1994, 38)At the start of that talk, Elder Scott stated his message would "apply to all present" and Elder Featherstone's remarks (linked above) likewise makes a point of including the adults.
The Kimball quote also directs members to 'abandon the habit'. Abandon is a strong word. It means to leave something behind for good with no intention of ever returning to it.
Myth 5: This only applies to men in the church
The idea that masturbation is a 'male only problem' is not true. Women are sexual beings as well and they are just as capable of falling into this trap as men are. There is no solid statistical evidence of how widespread masturbation is among men or women in the church but that doesn't matter. Casting masturbation as a male only problem heaps additional shame on women trying to deal with it and makes it harder for them to seek help when needed.
While many statements from church leaders reflect the idea that this is a male problem, not all of them do. Also, while the new YM/YW curriculum has done away with traditional lesson manuals recently, the Young Women 2 manual that was in use from 1993 up to recently covered the topic of masturbation in Lesson 33 (The Sacred Power of Procreation) and used the Kimball quote in doing so.
Myth 6: Sometimes it can be OK
Not that long ago masturbation was universally condemned by all Christian faiths. While the Catholic Church still considers it 'a grave moral disorder' much of the Protestant world has changed their position on it considerably. Citing that there isn't a specific verse in the Bible condemning, it many Protestants believe it is OK if your spouse approves, or is present when you do it, or if you 'masturbate without lust' (although that seems like an oxymoron to me).
It can be hard when military service, long term medical issues, or other circumstances prevent a married couple from being intimate for a long period of time, however there is not one statement from any General Authority at any time that says masturbation is an acceptable practice in such cases, or any other circumstance. Their direction to us is to never do that.
Myth 7: Those statements from past prophets are outdated
As you may have noticed, many of the quotes I've given come from the 70's and 80's. This was a time where societal views on masturbation were changing and it required the church to address the topic repeatedly.
It should not be ignored however that current church publication, like the Eternal Marriage Institute Manual, the New Testament Gospel Doctrine manual, and others make use of those quotes, validating the applicability in this day. I've also quoted Elder Richard G Scott.
On top of this Elder Tad. R Callister, as President of the Quorum of the Seventy gave a devotional address at BYU Idaho that was published in the March 2014 Ensign where he said: "The Lord condemns self-abuse. Self-abuse is the act of stimulating the procreative power of one’s own body" and then goes on to quote Elder Boyd K. Packer on the topic.
More importantly, statements like what President Kimball made do not come with an expiry date. We still quote Joseph and Brigham on many things. Only a subsequent prophet can offer clarification or an update to what President Kimball said, yet none have done so.
Myth 8: The church is trying to sweep all that under the rug and doesn't talk about it any more.
I have provided links to both General Conference talks and current church publications that repeat the same message that President Kimball made, often quoting him in the process. It does not get as much focus as it did in the past when the church needed to combat shifts in society, but it hardly hidden or ignored.
Myth 9: The church has changed it's position on masturbation
The position of the church is that it is wrong, the Lord doesn't approve, and that has not changed over the years. What has changed is that the leaders of the church are more aware of how sensitive this topic is for some people, and have given local leaders more flexibility in how to deal with it. Where in the past there was more of a top-down, one size fits all approach, local leaders are free to deal with each member on a case by case bases doing what will best help them to repent and overcome what is a potentially addictive habit.
Beyond the moral implications, I believe there are also ways it can be harmful to a marriage.
Masturbation breaks the link between sexual pleasure and your relationship with your spouse. If you can gain the pleasure on your own, then it removes a big incentive to resolve relationship issues, and it weakens your bond with your spouse since you no long have to rely on their kindness to have your physical needs met. The bonding effect a couple enjoys from sexual climax becomes diluted when that same climax is had alone. In this condition, it is much easier for a problem in the marriage to go unresolved as the couple drift apart. Each spouse's pleasure should be found in the arms of the partner, not in the palm of their hand or the tip of their finger.
C.S Lewis put it this way:
"For me the real evil of masturbation would be that it takes an appetite which, in lawful use, leads the individual out of himself to complete (and correct) his own personality in that of another (and finally in children and even grandchildren) and turns it back: sends the man back into the prison of himself, there to keep a harem of imaginary brides. And this harem, once admitted, works against his ever getting out and really uniting with a real woman. For the harem is always accessible, always subservient, calls for no sacrifices or adjustments, and can be endowed with erotic and psychological attractions which no real woman can rival. Among those shadowy brides he is always adored, always the perfect love: no demand is made on his unselfishness, no mortification ever imposed on his vanity. In the end, they become merely the medium through which he increasingly adores himself….
Masturbation involves this abuse of imagination in erotic matters (which I think bad in itself) and thereby encourages a similar abuse of it in all spheres. After all, almost the main work of life is to come out of our selves, out of the little, dark prison we are all born in. Masturbation is to be avoided as all things are to be avoided which retard this process. The danger is that of coming to love the prison."
(C.S. Lewis, letter to Keith Masson (3 June 1956); cited in Yours, Jack: Spiritual Direction from C.S. Lewis (HarperOne, 2008), 292-293.)
On the positive side, I believe if both spouses hold to the direction given by the Lord in this area their marriage will be blessed for it. If they focus on meeting their spouse's needs rather than their own it will draw them in both physically, spiritually and emotionally and a greater joy is possible from that then what can ever be found alone.