Actually ProtonMail does do this. They can't read your email so they can't know if you're actually abusing it via their terms of service. Thus if you file complaints against users ProtonMail will actually suspend the account without evidence until you clear your name.
There are a lot of cases but I'm at work and can't spend too much time collecting much. The gist however is that they are bound by Swiss speech laws, which are very ambiguous. "Inciting violence" is one such example, but of course, they can't see what you are supposedly inciting, so they suspend you.
It's abused fairly regularly in fact.