Technically F-Machine (and CHUD) only give a bonus to your overall sex skill. There's nothing directly involved in either that directly contributes to non-consensual intercourse. And sex skill doesn't actually help you rape people, seeing as you don't generally care that much about your partner's satisfaction when you're forcing yourself on them.
Actually the most direct rape-buff I can see would be the Brute Strength mutation. It gives you increased musculature so you can grab and hold on to people, and it gives a bonus to your wrestle skill which helps determine how quickly you can get the clothes off of someone.
Abominations also have a very interesting side effect for when they do the nasty with someone. They actually are able to use it as a combat technique of sorts (albeit quite unwieldy).
Yes, sex exists in the game. Yes, there are a small number of people who play pretty much for that reason. No, you're actually not going to see as much of it as it sounds like from the wiki and other external sources. There's of course nothing preventing you from going out there and selling your body to various NPCs for the sake of some occasionally absurd profit, and there are always the pornos for even more scratch.
I'm not going to say it isn't an integrated part of the game, because it is. But I do think you're getting the wrong idea of it, and I know for a fact that the wiki does not do a very good job of portraying the actual experience of playing the game.