The womens sexual control. 
There are manipulative men and women out there. There are women that would walk away from that situation and not ask for anything.
But it does come from weak men who will do anything for sex or female attention. Then they get screwed over.
I have no problem with something like the child support laws that a lots of guys bitch and moan about. If you have a kid you should pay for it, why should someone else pay for your problems.