I struggled with this question after I was saved. I viewed it as a placebo before I was a Christian. The reason is that it is not holy. You are driven out of lust to commit this act and it destroys you in time. Soon you become so self-centered that you cannot in anyway be able to have a proper healthy view of sex. I sometimes think that there needs to be a brother and sister forum for that we can ask these questions to our own sex if desired. God is against us trying to take our pleasure or our success into our own hands. If you commit this act then you are saying that my lust is far too much greater a need than to wait on you Lord for your authorization of sex. I struggle with this a great deal so I repent but there is nothing wholesome or safe about it. It will ruin your relationship with the creator and those around you because you are out for you gain. That's the best reason that I can give.