Why would a man or woman hate members of the opposite gender despite knowing that not all men or women are the same?

I'm guessing it involves not being able to relate due to different experiences and facing different double standards and stereotypes and forms of sexism. Also, I think it's human nature that women will tend to take their own gender's side just as men would do the same.
Why would a man or woman hate members of the opposite gender despite knowing that not all men or women are the same?
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