On the one hand, I can fully understand that nine-point-nine times out of ten it's just a metonym, that the majority of women don't mean it in a literal sense (although like janegrey notes, there is arguably a [sub]minority that do), that it's far quicker and easier to vent in one short phrase rather than listing out all the specific complaints against men and patriarchy you might possibly have, and that taking it too literally is often an attempt at derailing the argument and shouting down the woman.

On the other hand, though, looking at it purely as a rhetorical device, it is one that almost seems to invite that kind of abuse. I mean, purely as statements go, "I hate men" on the surface seems pretty simple and unambiguous, and is (apparently) hard to misinterpret. Particularly when its used in a context like this where the character/author (apparently) does mean it literally. So yeah, nine-point-nine times out of ten anyone who thinks the woman using it means it literally is just being an asshole, but as a rhetorical device IMHO it doesn't seem the most helpful in avoiding or preventing that kind of asshole to begin with,