Let's imagine for a second, that US and EU governments get together and for real ban all ads on social networks.

The end-user product of Facebook & Twitter majority of users interact with on a daily basis represent maybe ~20% of the tech that engineers are working on. The rest is some crusty under-the-hood tech geared towards collecting user information, selling/targeting ads, and rearranging your feed in a way that maximizes time you spend on the site. If there's no ads, all this tech is suddenly useless.

Facebook would immediately have to fire 80% of its staff. Its market value would plummet. They'd have to implement subscription model, that majority of users would immediately reject. Even if they accept a huge loss and allow people to use the site for only $5/y, I imagine only 10-15% of currently active users will accept it.

Now when maximising ads is not a priority, people start spending way less time yelling at each other on social media. They need to spend this time some other way.

I'm too lazy to think further, but it's clear that "just ban the ads" is a HUUUGE change that will affect so many things at once, that it's almost impossible to predict all effects it's gonna produce.