I'm fine with this feature if they implement a punishment system (which needs to include the LFD tool as well). There needs to be in-game player ratings similar to how Playerscore/Gearscore does that. Then after a player reaches some arbitrary number, like say -10, it would blacklist them and they would be unable to use either tool. Limits could be placed on it to prevent abuse, i.e. make it so players can only rate someone once or maybe once every 30 days or something. That way you won't run into a situation where someone gets pissed off at someone else for something unrelated to grouping and downrates that person out of spite. Or perhaps just make it so you can only rate people currently in your group, so anything that they would get downrated for would be related to that group.

This is the only real way to possibly deal with people being jerks in LFD and a possible LFR. People are going to be jerks regardless, yes, but as it stands right now, there's no punishment for it, so they're basically encouraged to be jerks.