I don't have time to write up a post, but I did want to point y'all toward this feminist discussion of rape fantasy.
Briefly, though, I will say that I've had rape fantasies most of my adult life. However, I gather they're not the same as most other women's. Mine are fantasies of doing the forcing, almost always to men. Sometimes they're simply violent (many of these are fantasies of getting revenge on male rapists by eye for an eye justice), and sometimes they are about forcing someone who is shy or someone who really wants to be fucked but couldn't ask for it because he's homophobic and thinks it would be emasculating.
I find that males are often a lot less troubled by these sorts of fantasy. I've never played one out, but many kinky men I've mentioned them to have responded with "oh, that's hot!" or "let's act that out!" rather than with intense fear of tripping emotional land mines. I think there's something to this: real rape is usually male-on-female violence, so my fantasy sounds a lot less real and a lot more like something to pretend for fun.
But personally I'm really troubled by the idea that someone who has fantasized about forcing someone else is someone who you should be leery of only for that reason. Shouldn't you be asking yourself why the person thought of it? Thinking about why you might fear that the person can't separate fantasy from reality?
In some cases I'm sure people can't. But... it just doesn't compute in my head how this might mean I'd actually enjoy doing real psychic damage to someone I like and am interested in. It's like saying that because I'd enjoy playing a video game deathmatch against my friends, I have a secret desire to harm them.