I'm a lot more sanguine about communities muting someone because they don't like that person than about companies muting someone because it's profitable to do so.

You can hypothesize a future in which Mastodon gets very popular, and in which a single for-profit node or a coordinated group of such nodes monopolize it and end up wielding censorship power similar to traditional centralized social media sites, but that's not what it's designed to do and there's no reason to assume it's a fait accompli.