I can see how collectivism can overlap between feminism and marxism, both have at least elements of group identity to them, and a certain element of grievance mongering exists within both.

With atheism though? I guess some people latch onto it for the sake of grievance with orthodox religion, which would naturally incline them towards that sort of marxist thought patterns, but there's a lot of atheists who just don't believe in the spiritual due to a lack of personal experience with it...

Sidenote: this lead me to an interesting train of thought (next time i'll take the bus, lol), groups like Antifa operate somewhere between a street gang and a religious meeting... If we treat their actions as religious rites, at least in a metaphorical/psychological sense, some interesting parallels emerge....