All sorts of discussion aren't possible unless the participants can be sure that the others are acting in good faith and not likely to engage in needless hostility or reprisals outside the discussion.

The term for this environment is "safe space", but they're unpopular for some reason.

I would rephrase that to say that "safe space" should be the term for such environments, but in practice that's problematic. The term was specifically invented to describe spaces where certain discussions are forbidden because they could be "triggering". It was not invented to describe a space where discussion is possible without unilateral escalation to unrelated third parties.

I suspect that a healthy society needs both kinds of safe spaces.

No, “safe space” has long been taken over to indicate spaces where people can be without worrying about being exposed to an idea that triggers a sensitive area for them regardless of intent or good faith.