> I've never understood how it's possible to be offended on someone else's behalf . . .
This may be true (that you don't understand), but I doubt it. If you have ever taken a stance on the wellbeing of people other than yourself, particularly a political stance, or if you have ever defended a friend or family member against an accuser, or any number of other normal human social interactions, then you do understand what it feels like, although perhaps to a different degree than me in this case.
And, I also have to point out that whether you understand why I argue about this has precisely nothing to do with the validity of my arguments.
> It's entirely reasonable to point out that women may respond differently to visual depictions of nudity
Only if it's backed up by evidence and relevant. It is neither in this case. Observing that women are less hairy is a fact, provable, and does not play a role in the argument at hand. Observing that women react differently to nudity than men is wrong on two fronts. First, it may not even be true. Second, in the context of a woman making a political statement about the depiction of her gender, it is a rhetorical device based on a premise of unknown veracity whose primary purpose is to discredit her beliefs to a male audience. It's a variant of "women are irrational, so we don't need to listen to them," albeit less transparently foolish.