Some people would probably assume that they won't have to do that, since PM doesn't really present their service as exclusive to people with certain political leanings (unlike, say, riseup).
Do you have other examples than the obvious white-pride hate-group?
Currently a human is making the judgement call to ban someone, based on their feelings. They could very well be looking at misinformation, but have no way of verifying.
The address banned could be completely unrelated to this hate group, maybe the hate group doesn't even exist, this is the point the poster was making. You easily can misinform, and get someone behind a protonmail address banned.
For future reference, since the OP is now gone, the address in question was YouWillNotReplaceUs@protonmail.com.