If everything was a free for all, that standard likely wouldn't exist, the market wouldn't exist in the same way, and advertisers would just be advertising where they can.
No, that isn't how things would go at all. It is far more likely they'd go with sponsored or created content, ideally with disabled ads if possible. Which works out well for the sponsor'ed creator(s), but it doesn't net the platform dime one. Assuming they do them at all. Because while it is deeply difficult to get positive attention to one's brand, it is remarkably easy to get negative attention. Nike, Coke, and all the other big spenders aren't going to want their ads on anything that might do damage, and if they can't get that out of new media, they will turn back to sources that can.
And if they were publishers, they'd be sued to death in weeks. Nothing with user added content can survive with publisher lability.
And even if you can't moderate political speech, you are going to have have take down methods for copy right or actually illegal content. And those mechanisms will be used to get rid of people.
To be fair, selling advertising space as a online business model has been falling apart across the internet as of late. Businesses have started admitting that they don't really get anything out of advertising online; almost nobody pays attention to them, and many people block them outright. The only exception seems to be sponsorship ads, which I understand have proven to be successful at pushing products to the consumer.
Marketing is disease, super effective initially, but we gradually build up our immune system. Sponsorship works because it creates that sense of I have given you a thing, and helped this person you are interested in, don't you feel semi-obligated to at least listen what I'm interested in.
You do realize you basically just argued that we should allow unethical and potentially dangerous practices so that big businesses can make money?
No, I'm saying that if they can't make money, they don't exist. Servers and infrastructure cost money. Unless you want the government or a charity to provide it, social media needs to make enough money to be worth the effort to create, maintain, and support. This is Capitalism, that's how it works. If you just want to burn social media down, then that's fine. But if you are arguing that being denied your social media platform is damaging enough, that it requires government intervention to make sure they don't kick you off, then I'm assuming you want it to live.