The latter. It's more than obvious that not all white people are racist, it's obvious not all men are sexiest, and it's counter-progressive to not focus on the actual issue. It's an attempt to undermine the experiences that someone has, and makes out that particular cause as something that shouldn't be talked about because not all X does Y. "911, some men have broken into my home and are threatening to rape me." "Well not all men would do that, I wouldn't do that."
Thank you for saying what I think about the whole situation in a much better way than I could formulate it and giving me a way to respond if someone brings it up in real life. I feel like telling those who say #notallmen that 1. I never thought it was all men an
2. That's not what were talking about.
But i doubt that would be as effective as saying what you did.