It is needful to recognize the principle of moderation which is all over the Scripture. Every single need we have can be met in a Godly way through the appropriate means. Food for hunger, drink for thirst, etc. But each and every good path to the meeting of needs can also be abused. Hence, we have gluttony, drunkenness, etc. The thing that is sinful in each case is not the use, but the misuse. The use is good and given by God for us to enjoy. So, I recognize the possibility of using masturbation in a similar manner, since there is no direct Scriptural prohibition.
Ok, I could agree with the "moderation in masturbation" theory. There is no mention of it as being forbidden (and I doubt it was an oversight lol) so if there is a practical use of it, perhaps. I didn't realize that I called the act a sin in my post. I thought I said that it would be a "sin to the marriage." I still believe this.
I don't know that I can go so far as to say that the "use is good and given by God for us to enjoy." Where masturbation isn't forbidden, it doesn't say that the action is from God. If anything, i would say that any kind of "replacement" of what God designed would be from Satan, who is the author of God replacement. Sex between a man and a woman is God designed. Self-sex was God's design or man's design? I am not saying that merely because it was not God's design but man's that it is sin, but neither can we say that "the use is good and given by God for us to enjoy."
If one spouse has a greatly lower libido then the other, I could see a possible use for it to help eliminate the temptation to wander.
The only problem I have with this is that God seems to have a solution for the "libido" issue:
I Cor 7:4,5 The wife does not have authority over her body, but the husband does, and likewise, the husband does not have authority over his body but the wife does. Stop depriving one another, except by agreement for a time that you may devote yourselves to prayer, and come together again lest Satan tempt you because of your lack of self control.
Certainly, there are going to be reasons for not wanting to have sex one night or even a short season. However, this should not be a lifestyle; it should not be the norm. There should be no reasons for a man or woman to have to turn to self-satisfaction when neither is depriving the other on a regular basis. We would then only be dealing with it being acceptable during the short periods of abstinence. I am thinking that when one is fasting and praying and seeking God (which is when they are permitted to refrain from giving sexually to the other), that neither are masturbating...LOL
I would question it's use within marriage, and advise a lot of consideration and openness between spouses. But, that would have to be endorsed by the spouse, and not done secretly. In that case, I would view it very similar to adultery, since it would then be secret sexual satisfaction without the spouse. Satisfaction is meant to be shared, whether actually physically, or at the very least, emotionally and with consent.
Agree 100% with the last two comments.