Its only safe if you're only talking to other people who also use protonmail. (Ideally also through tor.). As soon as your email thread includes people on gmail

Its only safe if you're only talking to other people who also use protonmail. (Ideally also through tor.). As soon as your email thread includes people on gmail, the government can just ask them for the email thread. And if you're restricting your conversation to people on protonmail for security, why bother with email at all? Seems easier to just put the conversation on signal anyway. And then you get all of signal's other security benefits, like E2E encryption, crypto ratcheting, disappearing messages and so on.