That's great in theory, but these companies heavily benefit from networking effects and become near-monopolies of their social network niche. You can't just switch to a different social network if you don't like it. And even if you could, it doesn't make it ok to screw people, it just means people can opt out of the screwing.

I'm not saying they are legally wrong, or violating anyone's legal rights, or that the government should do something. I'm saying that it's still wrong and unacceptable, and they deserve criticism.