Killfiles were local to each user which is good since each person could control what they saw. It was bad because new users who didn't know about killfiles would see the bad actors. It also meant that could have disjoint conversation so it felt like each thread was its own thing. You would have to keep telling people to not respond to the trolls.

The ideal is to have a global filter by moderators for the bad actors, and user killfile to tune that.