This tends to assume that each individual is a sincere member of a conversation, but real parties also don’t have swarms of robots and clones wearing disguises coming in to try to destroy your house. User reducing visibility is a strong first-line defense against bad actors that doesn’t require 24/7 moderators. If you poke through big, popular Facebook pages, like the NYT, and look through their comment sections, you’ll often find a ton of copy-pasted spam, scams, etc. (“this psychic saved my marriage! this accountant made me a bitcoin millionaire!”) I don’t believe the up/down system can be the only way to preserve the ability for people to have conversations, but we shouldn’t forget what problems these systems were created to solve.