Here's how I see it. There's things you need, your brain tells you you need it so the signal is extremely strong.
Take hunger for example. When you're hungry, you can be having the most fun in your life-but, you'll still eventually(usually almost imediately) make your way to the fridge/store/what-have-you because the signal is so strong.
Same thing with sex, your brain tells you you NEED to do this because repopullating is a good thing and one of the reasons you're on the world for. So, it's such a strong signal that people that can't get their hands on a wo/man(or choose not to) just masturbate to soothe the signal.
That's my point of view, more science then religion however.
All my friends are skeletons,
dulcimers and chariots
prayers to God, oh prayers to God
Was I sleeping all this time?
Was my shadow ever mine?Wintersleep-Danse Macabre