Wouldn't that go against the decentralized nature of the site?
No, it's exactly the opposite. The entire point of a decentralized federation is that while yes, the admin is in complete control of what content is allowed on his or her own instance, users who don't like what the admin is doing can just spin up their own new instances.
Ernest can ban this type of content if he likes. Others can take the kbin software and make a new instance where it's welcome. Ernest can choose not to federate with that instance if they continue to push content that's against his rules, but Ernest doesn't have the power to dictate the direction for hundreds of millions of users' experience like a certain centralized site's mad CEO or admin board does.
What would be against the nature of ActivityPub is if Ernest built something into the software to prevent it being used for types of content he doesn't like, even on other instances.
ripcord