For Twitter it really doesn’t make sense because it has become undebatably a “Nazi bar”, metaphorically since they aren’t an actual bar, but they still support and tolerate Nazis (and other manners of horrible people). Some people insist that it isn’t and there are “normal level headed people there” but that doesn’t matter, it’s still a Nazi bar, because it accepts and tolerates Nazis. How can someone expect to not be judged for going to and hanging out in a place like that?
I would encourage that, but if your instance doesn’t defederate them you may have to go a bit farther since you’ll still get replies from lemmy.ml users, as users are not blocked as part of this functionality. And that is by design, it’s not meant to act as a replacement or alternative to defederation, it’s meant to act as an alternative to blocking all communities on an instance.