Nobody is saying that they can't, mostly what you'll get is calls for defederation.

Calling for defederation is a matter of simply not accepting content or voting from the targeted instance. Everyone has the right to spin up an instance for whatever they believe, but everyone else also has the right to not pass your content through their servers or display it to their users

This isn't to call to shut them down, this is to raise awareness so people can update block lists, instance admins to investigate/check with their users/mods on what they want to do