There is a quote from Albert Einstein which I like to cite every now and then:
"Two things are infinite: the universe and human stupidity; and I'm not sure about the the universe."
He turned out to be wrong about the latter, but that's an entirely different story.
@smiley, To respond to your point, if you want to have a list you never want to play with, then you should have a private blacklist (and indeed you do). This is an personal matter. You have every right to decide you don't want to play a game with a particular player.
A public blacklist is an entirely different matter, though. People on that blacklist are people that the community as a whole does not want to play. If someone is put on that list, and the community agrees, then that's equivalent to a ban, only that he still has the ability to troll forum and games.
Plus, someone can change, especially in competence. In my first games on this site, I was totally incompetent. You wouldn have wanted to play me then. Now I have improved. And this is true for all of us.
So private blacklist, good idea (I have one myself, too). A private blacklist made available to the public, okay (I personally don't, but you can). A public blacklist, really bad plan.