Big Tech being a publisher means that their user-generated content would drop to the level of "Letters to the Editor" in the NY Times. Thus their revenue would dry up, too, because all those teen-agers walking around staring at their phones are doing so because they or their friends or someone they admire has content on there. They're not looking at passive media.
Or sites like Wikipedia, running mastodon instance, blogging, ..
Those who have money to sue, like Saudi Arabian government, Israel, or billionaires and lobby groups would have a field day.
They had writers. Usually those were not employees. They had to lawyer-ize everything they printed. If you sent in a Letter to the Editor, they had to scrutinize that, too, and call you to be sure you really wrote it.
If you're saying it's so important that people with no skill whatsoever be able to say whatever they want with no liability to the company that prints it; furthermore, that that company be able to monetize their content: I guess we're disagreeing. I don't think the world would be any worse off if that were no longer the case. In fact, we'd probably be better off.