You get a flood of people praising Hitler in your subreddit. 1000 per day You have two buttons in front of you: ban individual user (ban form takes 30 seconds minimum to load and fill out), and ban all from /HitlerLovers. Which do you pick.
That one can only do it within reddit is of course merely a technical limitation. The idea can be implemented much more broadly.
That alone shows that the hyothetical "you" is the last person who should be allowed to moderate anything.