I completely agree. It's ridiculous.

Most of my gothic mystery novels feature female protagonists. If anyone dismissed them as "women's fiction" I'd be furious for all the reasons you give here. And as you say, I'd be equally furious if someone dismissed one of my novels with a male protagonist as "men's fiction". Utter nonsense.

I get particularly enraged when I see people perpetuating this kind of gender stereotype with nonsensical remarks to the effect of "women don't like science fiction" or "men don't like romantic comedies". I can tell you that I am much more partial to romantic comedy than my wife is, and she is a lot more partial to science fiction.

Good stories in any genre are good stories. They are not "male" or "female".