We do have a pretty good idea of what would happen since the US has free speech protection in the constitution itself and it's largely upheld.
We end up with corporations like reddit and facebook doing restrictions instead. People naturally want to use spaces where they don't have to see things like gross images.
If private corporation would be barred from doing central censorship/moderation there would be a need for more decentralized filter services that block nasty actors and spammers.
We get like 10 attempts at spam every day here and it's tiresome having to remove that over and over again. If i just allowed that stuff here this place would be filled with spam ads and scams.