I get anger I get having morals but constantly changing emails as your main is exhausting. the features Proton offers for me have always worked and worked great.
The problem is that with the plans and ideas Andy Yen are proposing, it seems very likely that it will not work so great in the future. It works now, and I say that as a (non-paying) reluctant Proton user, and it is the best non-personal domain alternative out there, but "for now" is the key words here.
So the hatred is more of a warranted fear of the future (and of course hatred against Andy Yen being yet another carbon copy arrogant AI-techbro CEO).