I think a better approach is to make account creation frictionful (eg. charge money, set karma thresholds, require an invite, etc.), score each account, and ban

I think a better approach is to make account creation frictionful (eg. charge money, set karma thresholds, require an invite, etc.), score each account, and ban or time out accounts when they break community rules. But an even better approach would be to go fully P2P and leave the scoring and ranking and filtering at the end nodes, with the possibility of friendly networks of interest group peers assisting with the task. BitTorrent for social media, pgp signed accounts, fully flexible annotation and ingestion. It's also less subject to cabal-based censorship.