There are plenty of instances which forbid you from talking about specific topics, and no shortage of ones which block any kind of interaction with other instan

There are plenty of instances which forbid you from talking about specific topics, and no shortage of ones which block any kind of interaction with other instances which refuse to forbid specific topics - meaning that if you use that instance, you cannot follow users on instances which do not restrict discussion in the correct way and they cannot follow you. Some of those topics have included information that other Mastodon users would have really wanted to know about for reasons of personal safety, such as the latest alias and position of online power of someone trailed by a decade or two of rape allegations across multiple communities.