Rape is a specific crime carried out by men that is both derived from and contributes to male domination of women.
Agreed, Flora. And if feminists lose sight of this in the name of pushing some 'equality' meme we lose all hope of being able to correctly analyse and discuss this crime and its impact. We also leave women open to reversals, such as the one frequently deployed by abusive men, who often claim they are victims of domestic violence at the hands of their (beaten and terrorised) female partners, because she once tried to defend herself during a beating.
I understand what others are saying about their first response to anyone who claims sexual assault being one of compassion. And it's worth noting that when feminists insist on limiting the definition of rape to unwanted penile penetration, they aren't trying to minimise the harm of sexual assault, which can be just as traumatic as rape. But saying women can rape men is a basic denial of the material and social reality which underpins this act.
If women could rape men, if they could penetrate them against their will and forcibly impregnate them en masse, the world would look very different to the way it does today. Perhaps in some societies women would have even realised the potential their penetration of men had to harm them, then eroticised the harm, used it to control them through fear, forced men to bear their offspring, engineered social institutions that meant men had to submit to penetration by women (and the bearing and raising of resulting offspring) in order to survive, made it impossible for men to avoid submitting to penetration even though the bearing of those offspring frequently disabled or killed men, and created overarching social, spiritual and erotic systems of meaning that linked their penetration of men to men's inferiority... If all this existed, then it would make some sense to talk about women's rape of men.
We do no good at all by denying the basic material reality which underpins rape, which is the very thing that gives it both its ideological force and its actual force as a tool of harm and control, by pretending we can view it through a gender-neutral paradigm. Therefore, while it's natural to feel compassion when dealing with men's claims of abuse by women, the fact remains that they are not vulnerable to violence and sexual harm from women in the same way that women are from them, and we can't just treat their claims as if they were. I'm not saying we should lecture every man about sexual politics or legal definitions whenever he alleges sexual assault by a woman - if you believe him, then you believe him, and your actions would flow from that. The weirdness of the Shia LeBeouf situation is that clearly many feminists didn't really believe his rather strange story, and were twisting themselves into knots to make a show of believing it, or at least not doubting it, because they felt they ought to pretend he was interchangeable with a female rape victim and apply the same analysis to his claims.