That is a pretty good counterargument, and I do think that you should count that risk when evaluating Google's security.

But I think there are lots of other options besides ProtonMail that will do the same. (I pay $50/year for Pobox.com, personally, and vaguely feel like paying a bit of money for my email instead of relying on a free service is worthwhile.)

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.

It's abused fairly regularly in fact.

Hmm... Could you provide a source? I don't think they do this. At least not for paid accounts with a long history.

Can start here: https://twitter.com/protonmail/status/900097982212845570

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.

That's not a very compelling example.