Not sure if the blacklist has to do with keeping community nice - I believe the point of the blacklist virtue signaling to a) get around oppressive App Store behavior around Gab, and b) avoid dealing with European laws.

Both causes are entirely external to the Fediverse, and I haven't seen groups of "bad people" having to be cut off by blacklisting, so I'm not sure if I'm convinced that the list is necessary or effective.