The reason there's often backlash when a man says "not all men" is because its similar to saying "all lives matter" after someone says "Black lives matter". It's often said in a way that detracts from a conversation around women's struggles.

Also, from personal experience, if a women says something about men being the worst, or men are bad, it's not because they hate all men. My wife says men are trash all the time, but she married one. She says that because she has been victimized by way too many men. Harassed by a multitude of guys. I've seen the messages she's gotten, heard her stories, and just listened to her experiences as a woman. It's honestly worse than you'd think if you've only lived as a man. And now I say men are trash too.

And it's NOT all individual men, but there is an underlying culture of toxic masculinity that exists. There's healthy and positive masculinity too, but it's not seen by some women. I've been told by several women that I'm "one of the good ones" just because I'm doing the bare minimum to be a good person. That's not the norm, and I'm seeing that more and more in the people I'm around irl and online as well.

So it sucks being grouped in with villainous men, I get it. It was something I struggled with at first. But I know that some women have to default to "all men suck" as a defense because of what they've been through. And it's more beneficial for me to focus on being a good person and calling out shitty behavior, than arguing whether it's all men or most men or some men if I want to help make a positive impact.