This thread has little to do with new players, though. Nor even players who are unskilled because they're new. Nor, in fact, even casuals. That's not what it's about. What the OP is complaining about is how some truly terrible players have truly elitist attitudes, and it's sickening. Their performance is less an issue than their attitudes.
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@OP - I've always found that classifying players in an MMO is never as simple as "casual" or "elite". There's more than just two classifications. Generally speaking, the casuals are casual, and will rarely be seen in content as they may only run it once or twice a week. The elite are the elite, and they will be too busy being awesome at what they do to rant and rave in chat - these people are rarely found in PUGs. Then there's the people sort of in the middle - skilled, but too casual to really take advantage of it.
Lastly, we have what is by far the most obnoxious group of people. In my experience, a good 90% of people you'll find in PUGs fit into this group. I call them elitists. I use this term very differently from most of the MMO community, as they are NOT the same as the skilled few who are the elite. The elitists are the douche bags who have egos far too inflated for their very limited skill. These are the people who point fingers and play the blame game on the very first wipe. These are the people who will stand in AoEs and then complain that the healer wasn't healing them. These are the people who will pull before the tanks because "you should pull larger groups". These are the people who will hold groups hostage in order to be kicked so that they can avoid the punishment of leaving a group early. These are those people.
These people are the elitists (and I reiterate: this is not the same group as the actual elite), and they are the poison of MMO communities. I'd take a terrible but pleasant player over these elitists any day.