The problem is more complicated than that. Many banned accounts' comments aren't all bad. Unbanning them wholesale isn't an option if they're still going to break the HN guidelines. But killing all their comments wholesale isn't great either, if sometimes they post valuable things. So what we want is a mechanism that works at comment granularity rather than account granularity: let the good comments, and only the good comments, through. That's what this is intended to be.