[incongruity]

Is this confounded or bound up with things like fake news or bad science -- would I, if I owned a platform – call it π-Chan –be prohibited from banning users who espoused anti-vax ideas because I firmly believed they put society at risk (or whatever the justification may be)?

I would, on the one hand, be strongly supported by science, but on the other intolerant of others' who have differing points of view. Would I be allowed to run my platform the way I wanted? Whose rights would prevail in that case?

[moate]

The question is "who do you want to be your consumers" here. Both choices are PR choices. Legally, you're allowed to do either ("neutral platform" and "moderated discourse forum" are both things that are legally allowed to exist in the US at least).

If you want to appease the free speech crowd, you let the anti-vaxers stay (Gratz, you're running a Chan!) If you want to appease the intelligent discourse crowd, you ban/moderate people who violate your TOS (Gratz, you're running something closer to Hacker News!)