1) My family is on Facebook. I am not. ;-) It's already the case that Facebook, Instagram, and Twitter for example have different "crowds", though there's some overlap.

2) Somehow humanity survived without these networks pre-2007ish.

3) I have no problem with the existence of many smaller special-interest social networks. Those are manageable, and we had them before the rise of the BigCos. The problem is with the existence of a few all-encompassing, world-consuming, general-purpose social networks. They have proven to be completely unmanageable and toxic.

"Abolish Gmail", for instance, doesn't mean abolish email providers. Not at all. And it doesn't mean that "the next gmail" will replace it. Healthy competition is good, unhealthy monopolies are bad.