I do get that, but really, B doesn’t have any special sway. They’re just some randos saying that they don’t like A’s posting. While annoying, that’s going to happen on every social network. If I went on Gab and started posting a lot of pro-Biden content, I’m certain plenty of people would tell me to knock it off.
So sure, it’s alright for A to be annoyed by it. That’s definitely not a unique feature of the fediverse, though.
Party A says something on the Internet that offends party B.
Party B asks party A to self-censor/tells them to shut up, which offends party A.
Party A complains that they’re being asked to self-censor.
When party B is asking A to self-censor, there's nothing wrong with A complaining about what B is saying. If A's lying or being dishonest, oh well.