You can block instances yourself. Check your Settings then click the Block tab, then enter in the domain under Block Instance.
Defederating has wider ramifications and just because there are a few bad users or opinions people don't like doesn't mean that everyone should be blocking them.
We have a few of those users too who regularly get into fights or who might be classed as mean, so if that's the case then we would be blocked too.
Standards that one server has cannot be enforced by another server.
Also no dog-piling onto this thread which I'll be locking if it happens.