I'd guess that the need for genuine civil libertarians would go down with the witch density. The super majority of people is probably fine with seeing one witch per day, but they really don't want to live anywhere where they feel surrounded by witches.

The dynamics involved in city districts rising and falling and rising again might be similar. Online communities lack the rent-dynamic however. A "difficult" part of town gets more attractive because the rent is much cheaper. I don't know whether there's anything equivalent in online communities that would "gentrify" a toxic community.