All of the political extremist and hate speech instances should be defederated. And Beehaw just because them defederating us creates a really bad user experience if we don't defederate them as you could respond to comments/posts by beehaw users on other instances and not realise they won't even see your replies.
I don't know that mutual defederation is necessary, I think a clear warning that that user and users from that instance won't be able to see it would be enough. A red border on the comment with a hover tooltip explaining it seems like would work to me.