There was actually a discussion about this recently on Vagpag. Many women do have rape/being dominated fantasies (I'll admit this - I'm one of them). But the interesting point was brought up that in a fantasy it's never truly rape/domination because the one doing the fantasising is in total control over what they imagine.

For many it's barely connected to what they actually want from reality, which is a loving, equal relationship (there are exceptions of course, there always is). It's just a fun, deviant little thing to imagine.