I listen to a bunch of (far) left podcast to balance out my media consumption and the amount of bickering about purity is both amusing and slightly scary. Both the wide span of subjects (from racism, to sexism, to ablism, there's something new every day!) and depth ("it's not my job to educate you and here are 5 books about lived experiences that you should read before talking to me") is scary and genuinely interesting. For some people it almost seems like a full-time job.
We even see it in some other, non-political, social circles (knitting famously had a purity competition/obsession a while ago).
I'm still struggling to explain why this is such a focal point for some people. Perhaps this is a modern replacement for religious fundamentalism for some people?