A lot of people would say I'm transgressing my bounds if I try to use the influence I gained by paying for my server to threaten you into changing what content your server serves to your users. That's the essence of "block X or I'll block you."
And? They have a right to do so. In particular, they have a right to defederate any server for any reasons - which includes mine, yours, or this other person's, with or without asking things like "block X or I'll block you".
