I think most people have a fundamental misunderstanding of what social media platforms are and how they operate, all of which is laid out within the contractual obligations of the mutually agreed upon terms of service.
If you post something to say, Twitter, that is now their content that you have given to them for their benefit with the sole purpose of extracting value from the attention the content you handed over to them brings through the sale of advertising. That sale of advertising is what keeps the servers up and the engineers keeping it glued together paid. The surplus is profit distributed to the shareholders. This is of course an exchange where the value you extract stems from having your content amplified or enhanced in some way by their service. If for any reason any actor’s interaction with the service is determined to lead to a net loss, the only appropriate course of action is to remove that actor from the system.
The real problem isn’t a free speech or censorship issue, it is an anti-trust issue where a single entity has such an overwhelming control of a particular stream of media that their actions have excessive impact on the business and social ecosystems. Whether it is an anti-trust issue can be determined on how difficult it is for a competitor to establish themselves profitably in the marketplace. What sort of moats would need to be overcome to properly compete with e.g. Twitter given the monumental first mover advantage of that particular media stream... the media stream they created and proved?
In simpler terms, whether Facebook / Google / etc banning something they deem detrimental to their financial success having potential egregious impact on culture, society... whatever, is more a sign that these products have established themselves into the market in a way that’s fundamentally problematic and needs examination and effort to alleviate.
Should they turn into a public utility would change the entire business model and power dynamic and is not really relevant to what’s happening here. If for example the United States nationalized AWS and provided it as a civic web services infrastructure, free speech laws would be understood under a very different power dynamic. Censorship issues would be brought up and likely dealt with systemically, like not allowing the people running it from looking at what you’re hosting (you can organize a terrorist attack on the United States over the US postal service, by consequence of its intentional design).