The threads of high-profile users are where some people experience the highest engagement. Lacking that level of engagement on their own posts, they see the spaces of a high-profile user as a town square.
But it's not a town square. It's a salon, hosted by a person. It doesn't matter that we don't legally own space on a social platform -- each thread, ultimately, belongs to the person who created it. They have the right to ask anyone who joins in to keep the discussion on topic, or to watch their language. Perhaps more importantly, they have an obligation to the other people who have taken the time to make a thoughtful, on-topic comment. If someone runs into the discussion and begins attacking other people, or attempting to derail the discussion, as a good host, the original poster must take corrective measures.
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A lot of people out there believe open is better, that we ought to let people come in and say whatever they want, that we must make our spaces a true forum. I'm not one of those people. I believe, first and foremost, in creating a safe space for my readers. That means being vigilant. It means deleting "hiiiiii" comments that serve no purpose and lead the discussion nowhere. It means kicking disruptive people out. It means interjecting when commenters are having an argument and, if resolution is impossible, providing a level of moderation that enables them to say what they think without attacking one another.