First off, what exactly is this "attunement removal" thingy? Well, one of the changes in patch 2.4 is that you will no longer need to complete a lengthy attunement quest in order to enter Mount Hyjal and the Black Temple.
What do these attunements require as of patch 2.3? The Hyjal attunement requires that you've completed Serpentshrine Cavern and Tempest Keep: The Eye. The Black Temple attunement requires that you've completed Serpentshrine Cavern, Tempest Keep, and Mount Hyjal. This means that there's a clear line of progression. Serpentshrine Cavern/Tempest Keep rolls into Mount Hyjal, which then opens up Black Temple.
The overall order of progression goes something like this:
Gruul's Lair, Magtheridon's Lair, Doomwalker, Kazzak, Zul'Aman
Serpentshrine Cavern, Tempest Keep
Caverns of Time: Mount Hyjal
With guilds moving down the list, starting at Karazhan and finally ending at Illidan (or disbanding at some point in the middle). After 2.4, people will not necessarily need to do any of the bits in the middle.They could, for example, go straight from Gruul's Lair into the Black Temple. They'd wipe on their first trash pull, or, if they were really lucky, they'd bang their heads against Naj'Entus until they beat a bit of sense into themselves, but they could still do it.
There are arguments for and against attunement removal, which I shall attempt to summarize here.
What are the arguments for attunement removal? Well, an acquaintance of mine is in a 5/6 SSC, 3/4 TK guild who have gotten Vashj down to 63%. He was talking to me about his guild's progress, and happened to mention that they would use gear from Mount Hyjal to down Vashj. The attunement change would help guilds who are stuck on Vashj and Kael'Thas to progress by giving them a gear boost that would be somewhat easier to attain.
The attunement removal will make raid content more accessible. This can't be a bad thing - Blizzard obviously wants as much of its consumer base to experience that endgame content as possible, and making it easier obviously means that people will progress through it faster. This makes it easier on players who are new to raid content to achieve their goals before Wrath of the Lich King comes out, and increases the likelihood that players will be able to enter Sunwell Plateau at all.
Accessibility has always been one of WoW's greatest strengths. Any idiot can pick it up and play it - just look at your last PuG to see how true that statement is. The death penalties are trivial, the learning curve is gentle - hell, the game practically leads you along by the nose in the starting areas, especially now that you can see questgivers on your minimap. Therefore, any move to make content accessible is logical, considering that accessibility is one of WoW's biggest selling points in the first place.
Moreover, the fact that you can waltz into Black Temple and Hyjal whenever you please gives players more choice. Choice is a wonderful thing. I like that we can skip a few bosses in Karazhan to get to Prince quickly because our main healer is on a tight schedule (although I would've liked to have had a shot at getting my tentacle staff of molesty doom last week, but downing Prince was a huge morale booster). I also like the fact that we will be able to, say, spend one night in Hyjal and get a gear upgrade or two to help out with the whatever boss we happen to be stuck on at the time. I would love to have even more choice, in character customization for example (and that's one of the reasons why the introduction of Inscription in Wrath is one of the things that interests me the most).
However, it's not all roses and fluffy kittens that poop rainbows. There's the argument that comes from everyone who has already completed content that gets subsequently nerfed: "It's unfair that they get to go right into Black Temple when we had to do the attunement for it!" It's along the same lines as people who completed the attunements for SSC/TK before they were removed too - and people who killed bosses that later got nerfed.
Personally, this isn't too much of an issue for me, since all those people get bragging rights: i.e., "I did it when it was still hard, noob!" Things get changed. I would be irritated if all my hard work was rendered void too, but think of it this way: all those people who are already in Mount Hyjal/Black Temple are way in front of guilds that aren't in terms of gear, teamwork, co-ordination, ability to deal with technical encounters, and so on. Not only have you progressed further, you have proven that you are capable of getting into the hardest raid content without the need for Blizzard to unlock the door for you.
This is the problem I have with it: skipping bosses. Guilds will be skipping bosses until they have farmed enough gear from the first few bosses of the next raid dungeon until they have the gear to make the fight they are stuck on easier. Some guilds will skip Vashj and Kael altogether - hell, even Archimonde - and just try to get all the way up to Illidan without downing any of the other main bosses.
Guilds that try this will fall apart when they get to the point that there is no easy gear for them to leapfrog over to. That, or they will have to admit that they have to pull their act together and learn how to do a technical fight without going, "oh, this is too difficult, let's go do an easier boss with better loot instead."
And the people who do attempt to gear up by leapfrogging, but actually do go back and take out the bosses they were stuck on. On the one hand, this seems cheap to me - getting better gear and going back to blaze through content, like doing heroics with a group all in Karazhan gear. On the other hand, it's still easy to wipe if you don't know the encounter - like in Heroic Mechanar, when you don't know that standing next to someone with the opposite polarity will be deadly. Gear, after all, is no substitute for skill and knowledge. Put someone who's never played the game before in full tier 6 and a lavender mageweave shirt and enjoy the show.
On the other hand, I use flasks and other consumables in my current raids. Is that 'cheap'? Of course not. Getting a few pieces of gear is just fine - it might give you that extra edge, like a flask of fortification, that lets you down the boss. What I would have a problem with is if we, say decided to only do Prince Malchezzar once we'd gotten Black Temple/Hyjal gear. That would be cheap. So, say a guild is stuck on Vashj and decides to farm the first few bosses of Tempest Keep, mount Hyjal, and Black Temple... then, once they've got six or seven bosses' worth of gear, they come back and trounce Vashj. Is that cheap? Is that guild going to fall apart as soon as they get to Archimonde because a gear check isn't good enough anymore? It's interesting.
Having said all these things, let's consider that Gruuls' Lair, Magtheridon's Lair and Zul'Aman are all without attunement, while Karazhan does still have an attunement. Are people going straight into Zul'Aman, Gruul's and Maggie's? No, of course not, they'd get trounced without Karazhan gear. Having said that, most (edit: changed from "all") of the bosses in Karazhan are manageable even by a guild that's never raided before. The fights in Gruul's, Maggie's and Zul'Aman are all much complex - whereas Winterchill is an easier fight than Kael'Thas. There is no temptation to go straight to Zul'Aman because doing Karazhan is the logical step. Is farming Hyjal and Black Temple gear now going to be 'the logical step' now? We'll see how the raiders handle this once Patch 2.4 comes out.