So, I’m answering this without all of the context. But I think that their statement could, potentially, make sense for some instances. I don’t think it makes sense for most/all general instances.

But imagine, for example, an instance whose sole purpose is pornography (seems like the easiest example). All communities created on that instance show pornography and nothing else. Now imagine someone joins that instance who is completely against porn, and all they do is complain about the porn and report posts for being porn. I think that the admins would be within their right to remove/ban that user for not aligning with their instance’s purpose.