Once you start hosting an instance that has open registration, it’s not just “their house” anymore. They are providing a service to people. They do so willingly. Arbitrairly blocking instances because you don’t know how something works and don’t bother to check it isn’t the way to host a free and open instance.
You seem to be uniquely bad at reading so this is comment is the start of this subthread you originally replied to. Nobody ever suggested they COULDN’T implement any rule they please. It was never a point anyone brought up for you to be refuting. It is literally you dishonestly trying to steer the discussion away from the actual point of discussing SHOULD they.