I don't believe tanking is significantly harder than other roles in WoW for a halfway-competent player. In Cataclysm content all players are generally required to deal with fight mechanics, the tank is just the guy getting hit in the face while it happens. The major difference in my view is the expectation of a large proportion of the playerbase that the tank also needs to lead the group.
There's a reason for this. Tanks are natural group leaders, leading the group literally in terms of the gameplay itself. A well-geared tank who knows what she's doing can lead a group without saying a word, brute-forcing everything with the DPS following her lead. The problem only exists when the tank is not able to lead the group, and for some reason nobody else will.
This is the attitude which is discouraging people from tanking. I've been in plenty of PuGs that did splendidly with an undergeared and inexperienced tank because just one of the five players took responsibility to co-ordinate the group.
This is something that Blizzard has attempted to build into the LFD system. You know that little "Leader" crown icon you tick without thinking when you queue for LFD? That's you volunteering to lead the group. In practise, though, all it really does is give one group member different coloured chat text. And while many people don't have a problem with barking orders at other people-- suggesting that they at least think they know better than the rest of the group, only a small proportion of people seem willing to take on the responsibility of actually leading that group.
You can see this lack of responsibility in the public chat channels, with people posting every five to ten seconds along the lines of "Hunter LF raid". To me, those three little words paint a broad picture: "Although I'm too lazy to try to put together a raid myself or even seek out an existing group past posting three words in a chat channel, if someone else would like to put the effort in to recruit me, summon me there and lead the group I'll gladly press my buttons to receive loot."
The sad thing about the state of WoW at the moment is that a lot of the recent evolution of the game has been to cater to this type of player; to put them as much as possible on the same level as the people who can and do put effort in. In creating the LFD system, they gave players otherwise too lazy to seek a group on their own push-button entry into dungeon groups.
I don't blame Blizzard for this-- they're a business and those people pay the same $15 per month that I do, and so it's in Blizzard's best interests to keep lazy players happy customers. But this is negatively affecting the gameplay of those who are and have always been willing to put effort into the their group play.
Someone look at me straight faced and tell me it wasn't faster for a DPS class to assemble a Heroic group before the Dungeon Finder made it "instant". You asked in trade, you did a filtered /who, you whispered people and you started your own group. It required more effort, but even as DPS if you were willing to lead in that way, you got a group in 5-10 minutes, depending on the time of day. And since it was your group, you didn't even need to pass a vote to remove any fuckwads you might have accidentally picked up.
So how did we all get roped into this LFD system when doing it manually is so clearly superior?
I blame tanks.
I'm laughing now because those are three words I never though I'd ever use in that order. But bear with me:
As a tank, you are the bottleneck in the system, so you have the power. You push a button, you get a group. If the group was crap, you could probably still carry them... but if you found you couldn't, all you have to do is refuse to pull until they boot you and you can get another group with another button push. Nothing speaks for the broken-ness of the LFD system quite as strongly as there being a purpose and a benefit under the current system for acting like an ass.
But really I can't blame tanks for long before I have to trace that blame back to this LFD system that supports them universally no matter what they do, a system soon to provide even more support via additional rewards, so there's not only little reason for tanks to look outside the LFD for pick-up groups, they are being actively encouraged not to. And with zero tanks outside the system, anyone who is still willing to create and lead their own PuG can't find one, and their only remaining choice is the LFD system...
The disturbing thing in my opinion about this new system, and something I don't think many bloggers I read have realised [because they would be whinging about it if they had] is that Call to Arms may cause a tank to refuse to run randoms with their own guild-mates, because queueing as a group would mean he didn't get the extra reward.
Attaching rewards to an antisocial system results in people being rewarded for being antisocial in WoW.
This is seriously blowing my mind right here.