Intolerant ideas (including messages and posts) should be allowed, considered, and countered with better ideas. Should be easy, since intolerant ideas are generally shitty ones.
Indeed, such ideas are often baseless, but the people who hold them can still be resolute against rationale, as per Karl Popper's quote in the wiki article above:
... for it may easily turn out that they are not prepared to meet us on the level of rational argument, but begin by denouncing all argument; they may forbid their followers to listen to rational argument, because it is deceptive ...
Intolerant actions (and I’m differentiating against speech from action here) should be prevented.
I'll preface this with my personal opinion here, that corporations do not merit civil personhood, yet I think focusing on free speech is veering away from the question and hand: in particular, how should the Fediverse (or at least our instance in particular) respond on engaging with Facebook, in light of what we currently know of the corporation's historic actions, as well as our uncertainty of it's future actions.
I suppose we could also rephrase this question more generally. I.e how should Fediverse communities respond to the hypothetical approach of other social media conglomerates, supposing the Fediverse gains the attention of not just Facebook, but also:
- TikTok
- YouTube
- etc