My feelings on the above are likely contingent of the nuances of implementation. Do downvotes ultimately censor posts? Are votes equal weight? Etc.
From a higher level, I'd grant that (a) platforms have a fundamental right to try to realize their vision, which may include promoting and demoting various types of content & (b) spam and astroturfing is a constant reality in any social platform (and users are better served by less of both).
So I think there are justifiable reasons for censoring, or at least decreasing visibility. I've been on forums long enough and have too low an opinion of the average internet denizen to think otherwise. :-)
Hence, to me, the emphasis on ad vs post hoc restraint.
If I allow you to make speech, and then, on the basis of that piece of speech and NOT on your identity as its speaker, decrease its virality in a way that's still fair (e.g. yank it from feed promotion but still allow direct linking) and then (in rare cases) absolutely censor it, that feels fair. To me.
If I proactively identify you, godelski, as someone likely to say *ist things and consequently ban you or pre-censor everything you post, irregardless of the individual pieces of content, that does not feel fair. To me.
As well, and I should have punched this more in my comment, as emphasizing "individual." Which is to say "1 human person, 1 share of public speech rights."
IMHO, if free speech is a right that flows from our existence as sentient beings then it's difficult to get from there to "you deserve more / less free speech than I do."
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And finally, because I know I'll get this response eventually, yes, I know playing whack-a-mole with bad actors on a public platform is a nigh impossible task. I've done it. Maybe actually impossible.
Tough.
Uber skirted labor laws in pursuit of profit. Social media platforms are doing the exact same in terms of nuanced moderation in pursuit of profit. "It's difficult" or "It costs a lot to employ and train the headcount required to do it" isn't an acceptable defense, and we shouldn't accept it.