The more popular a community becomes, the shittier it gets. The easier you make it to join and interact with, the more popular it will become.
In the case of places like Gab, Truth Social, Parlor, and other right wing nut job havens, while the quality of users might not get higher if you raised the barrier to entry, those places certainly wouldn’t have become as popular as they have.
But the barrier to entry isn’t the only reason they’ve congregated there, they have other cultural reasons driving them, primarily the owners or moderators being friendly to that kind of mindset. I don’t think the same crowd would be able to gather here as they’d just get defederated.
I disagree with that. The larger subreddits have significant moderation problems. Only through extraordinary efforts by the mod teams, such as at /r/askhistorians, are things kept in line. It's simple math: the more users you have, the more likely you are to have people posting in bad faith. If a subreddit of 1 million users has only 0.05% of its users posting low quality content, that's still 50,000 people that need to be moderated for.