the discussion is happening here: https://github.com/7c/fakefilter/issues/73
Someone working at Proton has commented on the issue, the list maintainer wanted to take the discussion with proton private so we have only a few posts from them.
If you want my personal take:
It's very clear how the list maintainer opposes anonymity in the internet in any form, which I see as an attack on freedom, journalism and activism.
I'm not a fan of Protonmail of any sort and in fact I consider that their privacy is lacking... but I really hope they can talk some sense into this guy. This block list seems to be used by a lot of webs that will start blocking virtually every private email provider.
(Edit: I assumed the person that posted the email list was a maintainer, but they don't seem to have a "contributor" or "owner" badge, so idk. Maybe they are just very angry at privacy and anonymity on the internet)