You're correct in that it's really a market capture problem as things are. But the popular proposals that try to co-opt Big Tech into the censorship game are popular precisely because of that market capture - it's a way to make it extensive without putting the government in charge of it explicitly.

So we can't really treat these two as completely separate right now. Indeed, if those schemes are allowed to go forward, the next thing you'll hear is that we can't break Facebook etc up, because doing so will limit how effectively some information can be suppressed. The more power is concentrated, the more it seeks to sustain that state of affairs, and the better it is at that - so why would we hand those companies so much power when they already are a major problem?

Who decides what's off limit?

Whoever makes that decision for each platform.

There're certainly multiple places one could draw the line--the efficacy of a given position for these sorts of things varies by your objective or simply the severity one perceives.

Thanks a ton for providing the opportunity for some discussion on this!