Casual sex, I don't see the problem with. Are the people who are against casual sex here also against masturbation? Because really, that's the point of casual sex. It, in the psychological realm, is basically like extremely enhanced masturbation. You've got two people who are sort of friends, both find themselves wanting sexual release (the reason we masturbate), why would they use their hands when they could just as easily use each other? As long as both parties realize that it only is just super-masturbation they should be fine. And those two people have probably mutually agreed that they're okay with it, in which case people who argue against it are just trying to force their morals into other people's faces.