Yeah, at the moment companies are pretty free to refuse service like this, based on their own policies, but I think there’s a decent argument for a legal framework. The biggest tech companies are indeed a core place that communication happens, I believe formalizing what types of content should and shouldn’t be moderated could be a good idea.
This would be very contentious, though. Many, many Americans would be strongly against the government telling private companies how to moderate speech on their platforms. It may even be unconstitutional - would a formal, legal framework represent the government restricting free speech?
