I would say quite the opposite. Because mostly you get people in the group from other realms, there is (for them) no reason to be polite or play as normal people.
Most of the times I was tanking or healing and i started to develop a deep hatred against DPS classes, especially hunters, warlocks and rogues.

They rush you, their only conversation usually is just “hurry hurry” or complaining about various things. Basically, you can shrink the whole experience into 2 points of view >
as tank – they rush you if you pull only 1 group of mobs at once. sometimes even get it to the point they don’t wait for tank to pull, but pull mobs before you had a chance to develop some threat or start pulling other group of mobs while fighting one.
as healer / buffer – once you enter the instance, you start to buff, which depletes your mana pool, but the group already pulls first mobs. something like mana-break is rarely seen and rarely achieved. mostly, the tanks do cooperate, however there were times, when i was drinking, tank was waiting for me to get mana and the huntard pulled, because he was bored.

and ninja-looting…bigger problem than ever.

my solution >
as i usually play one of the key roles (tank/healer) – if there is someone ninja-looting i vote to kick them or leave right away. what comes if tank leaves mid-fight – everyone knows (wipe)
it also happened to me 2 times that i joined a PUG, saw a huntard and directly said “Either kick the hunter or i leave” and the rest of the party kicked the hunter. it’s hard to get a tank, but easy to get a stupid, ninja-looting, not cooperating huntard with a stupid pet set on “agressive”