I've never understood it. I just don't see the punchline.
How Is "Kill All Men" A Joke?
edgy = funny to some people which is fine. Others are just sexist feminist radicals. Ultimately the same reason "kill the Jews" is still a thing.
It's the same kind of "joke" as saying "all idiots deserve to die".
It's the same kind of "joke" as saying "the only good injun is a dead injun".