Ever been that one person that was the cause of failing an Immortal or Insanity run? The Immortal/Insanity achievements being used as the measuring tool of progression is a huge mistake on Blizzard's part. This design inevitably creates hatred/disappointment all aimed at one (or sometimes a few) individual(s). There are better ways to determine guild progression. And Blizzard has already used two other methods that didn't result in such catastrophe.

2005-2008

When World of Warcraft was first released, the measuring of raid progression was very simple: What bosses have you killed? While the most common statement said about this is: "Raids were more epic back then", this was an unhealthy route to take endgame progression after the game became too popular. The discrepancy between hardcore raiders and the rest grew larger as time went on, while new bosses had to keep being developed and released. You both alienate the majority of your playerbase AND have content that your developers have invested a large amount of time(money) on that a very small portion of your subscribers are getting to experience. This goes against the interests of both the developer as well as the majority of the gamers.

Under this progression design, it'll become immediately clear that there is no limit to the amount of time their guild/raid can invest into progression. The pressure to compete will always be there for any gamer. Under this pressure, there will always be more time you could spend raiding. This leads to burnout and potentially the death of guilds containing plenty of capable players.

Timed Clear

At one time the pinnacle of progression was the Zul'Aman Time Clear. This was the first time there was emphasis on speed and efficiency. With this, you're going to have people that are pushed just as much, but with a much healthier atmosphere. In this environment you're going to see that it will no longer be up to the leader to motivate players. The design itself will motivate them. There will be less politics as well as less individual ego. If you fail these timed runs, players still get a reward for their time and there is almost always going to be less blame on certain individuals. While certain players can mess up, there's always more the rest of the raid could have done better. Extreme RNG will also play a smaller part because a skilled group can recover from those extreme situations.

The non-hardcore players will still get to experience the new content that Blizzard has designed for them, the rewards will simply be less significant. Their accomplishments relative to the hardcore will seem less trivialized and drive to improve will increase. What does a player that was unable to complete the Zul'Aman timed trial say to themselves when they see a ZA bear now? Probably something like, "Damn, I wish I could've done that." With no blame on luck involved.

The Present

With the release of "Wrath of the Lich King", a brand new design was implemented to test and measure the high-end guilds. Now that the achievement system has been implemented, the measuring of progression will became "Who has done the hardest achievement?" Blizzard made these consist of "Immortal" or "Insanity" types. Depending on the achievement or instance, this either means nobody can die (Immortal, Naxxramas) or the run has to be completed without wiping at all (Insanity, Trial of the Grand Crusader). Blizzard wanted something hard/meaningful for high-end raiders to obtain. The most intuitive idea at the time was: "Clear the instance with no deaths or wipes."

First, this design bumps into fundamental problems that the internet has, much more than other designs, such as latency and connectivity. Also, RNG is going to cause either unavoidable (or near) deaths, yet the game needs RNG to keep it from being stale or too predictable. Under the event of failing one of these achievements, you're going to create a "guildy vs guildy" atmosphere, irrelevant to the amount of blame that there should be. You're also not even guarenteed quicker runs with these types of raids. Meeting the criteria of "don't wipe/die" is going to be easiest met using a "slow but steady" mentality depending on the specific encounter. In those cases, it will simply be less fun.

End-game World of Warcraft has gone through many phases. Timed runs create a more positive environment for all the player-base. And from a developer's standpoint, it's MUCH easier to tune/nerf by simply adjusting the time allowed. This game needs to challenge people, not defeat them. It should be clear that the Immortal/Insanity-style achievements should stop being used as a measurement of guild progression and that other methods should be pursued.