Jerks will be jerks because there is simply no penalty.
A jerk who wants the rewards will be nice for a while, and once he has all the rewards he wants, he turns back into a jerk again. He may even proudly say, "finally now I can be myself again".
The only way to suppress jerks is if they face very real and immediate threats. Such as GM action (which is costly and impractical), or peer sanction. Peer sanction will only work under local-server matching. The sheer number of people in a cross server matching service makes any blacklisting ineffective.
But then any "down-voting" mechanism can and will be actively abused by the trolls, so it's a good idea not to have that.
In the end, I suppose we can only rely on the 2.1 LFG Board to go live. Those who don't mind jerks or are jerks themselves can troll cross server. The rest of us do only local parties, and by blacklisting the jerks in our own server, we eventually will weed them all out.