The fact that messages concerning the dangers of making yourself vulnerable are not communcated equally amongst the sexes is a form of subtle sexism... if advice is to be given it should be done evenly and not focussed on women.
However, just because there's a problem with how messages tend to be skewed towards women doesn't mean the message itself is invalid.
I will tell both my son and daughter to be careful because being paralyticly drunk is dangerous and risky whoever you are.
As for the argument that rapists would rape anyway... I'm not sure that's true for crime. Make it more difficult and you probably do dissuade some, the same for any crime.... I don't hear people say, "burglars are going to burgle anyway, so why bother with keys!"