Social networks do not have to be natural monopolies! That's where federated open protocols come in, like the #fediverse. And in a federated network of small to mid sized instances moderation is a more tractable undertaking, and users can chip in to keep the sites running as much as they're able to. There's room for different funding models here too.
#Mastodon seems to be headed in the right direction, though we probably also need #dataportability - a way to easily move one's data from one instance to another as some will inevitably cease to operate (or someone just feel like moving), in a way that preserves one's network graph.