Section 230 has nothing to do with impartiality or freedom of speech. It just lets any forum or social media platform actually exist. If Section 230 wasn’t there, every post on Facebook would have to be cleared by their lawyers, before it could appear online!
The same for this forum, @Leo would never be able to run it without Section 230. You would have a bunch of private, invitation-only forums, if any. No support forums, no help forums, no reviews on shopping sites, no reviews of restaurants and businesses etc.
They aren’t content providers or publishers, they are content enablers. The only content they generate are official notifications to users about changes in service etc. You could possibly include announcements by Zuck, but that is, in theory, his private account.
What any forum or social media platform allows or disallows is purely up to them. If they don’t like a subject, they can ban it - just think of the breast-feeding scandal on Facebook several years ago. I can go into town and see dozens of women breast-feeding on the street, but any photo that shows that is banned? The wedding pictures from my daughter would have been banned, because her sister-in-law was in the background breast-feeding her son, it is a natural act and enhanced the photo - 3 women with their children, one standing next to the mother, one breast-feeding her 3 month old baby and one pregnant, a lovely shot, but banned according to Facebook’s old policy.
But that is Facebook’s decision to make. It decided violence is fine, but the human body is off limits. There is nothing users can do, apart from not use the platform if you disagree with them. There is nothing written anywhere that says they have to publish anything anyone writes - they are not a federal US Government institution and therefore not beholden to the 1st Amendment; that would only come into play if the US Government told them to ban specific topics, and it would be the US Government that would be prosecuted, not the social networks.
If you don’t like their policies, don’t use their platform, go somewhere else. I did, I have actually blacklisted all Facebook domains (over 2,500 of them at last count, including Instagram and WhatsApp) from my network.