What are the criteria for when a private site crosses the line to become a "public" site where it is no longer allowed to moderate its content (or has to modera

What are the criteria for when a private site crosses the line to become a "public" site where it is no longer allowed to moderate its content (or has to moderate its content based on federal rules)? If it's based on average users over a time period, do we trust the site to report it accurately? If a user gets banned from a "private" site that has not yet hit the size threshold, and the user complains to the government and alleges that the site actually is big enough, does the the government go in and audit the company's logs to make a determination over whether it should be a "public" site? If it's based on something looser, like "percentage of people who use this site as their only news source," (which does seem more defensible, to me) how do we set up the criteria for making the determination? Also, how would the federal rules for content moderation look? Would a call for open insurrection still be bannable? What if two roughtly equal portions of the electorate don't agree about whether it was a call for insurrection? Who decides if it was? I think questions like these need to be thought through and answered before we can seriously talk about making a law that prevents social media companies from banning anyone they choose.