If I look at this (World of Warcraft player angst), I see two factors here that are the problem: The first is that people only consider raiding fun if it is successful, and fast at that. That is a development of the video game age, affecting younger players far more than those over 40, like me. I grew up on board games and pen & paper roleplaying games, which worked on very different basic premises: In most board games only one out of several players wins, which teaches you to enjoy the act of playing the game, because you simply can't win all the time. And in pen & paper role-playing games you don't really win at all, and again do it for the fun of playing. It is only single-player video games which ended up teaching people that it is possible to win every game, and even necessary to win every stage to advance to the next one. With that video game mindset, it is obvious why somebody assembling a pickup group insists of only chosing those players which have the biggest chance of success.
Actually, this is frighteningly applicable to our testing and accountability regime:
Let’s get one thing out of the way: I hate GearScore. I hate it. Hate it. HATE it. It sucks. It’s an arbitrary number that an addon assigns to my character in order to determine my worth as a player. Not to mention that it’s a broken system that is too easy to exploit.