Where did you get your information that "rape is a pretty basic sexual fantasy--of both men and women"? While being dominated may be a common fantasy (and I'm not agreeing that it is), domination is NOT rape. Since rape is, by definition, done against someone's will, it is a paradox to say someone has a fantasy about being raped. And if the person has a fantasy about being the rapist, that does not make it right, or normal.
Joking about rape, having videogames about rape, etc, create a "culture of rape" - where it seems less important, or bad, than it really is. For instance, if you make a joke about "slapping a 'ho" - it makes it seem slightly more ok. Sure, 99% of people wouldn't take that step, but the other 1% will. As for GTA, 99% (or 99.9%) of people won't go out and carjack a cop, but it does desensitive us a little to violence on the road. I'm seriously generalizing and simplying here, but hopefully you get the point.
I really hate the slippier slope argument, since as complex, nuance-able beings, I like to think that we can think enough to find lines to agree on as a society.
I'm not suggesting that we should legislate against it, since it is already banned by the major retailers, and like others, I think a ban (and this article, I'd never heard of RapeLay before this) raises the visibility - and interest in - the game. But that doesn't mean we can't have a frank discussion (among ourselves, with our children, etc) about what rape really is, and why a game like this isn't acting out a "common" (and thus implied normal) fantasy.