I agree in principle but if it ends up with defederation-by-default, or something similarly restrictive, you'll kill the whole point of the federation and we can just go back to Reddit. IMO it should be used very sparingly (mostly to combat full on spam kinda like with email) and largely let the users themselves decide.
OP rants about seeing garbage from garbage instances but if you actually subscribe to the communities you want, you'll only see comments from those "garbage instances", and there can still be decent people with interesting viewpoints on there.