TL
R - People are jerks.
Here is my two cents on the matter.
I ran ToT on LFR yesterday, just looking for a shield upgrade for my tank. The other tank was new, did not know the fights, but was very polite and we talked before each boss pull. We do the first and second boss in one pull, no problems, no deaths.
Next we come to Lei Shein. We have one miscommunication on moving the boss, and raid damage results in a wipe.
Cue the ensuing verbal harrasment that reads something like:
"OMFG TANKS WTF WTF!!!"
"Horrible tanks"
"Effin' tanks make it harder for the rest of us"
And so on, and so forth. The first tank and I chat in private, we discuss the issue. We pull again.
This time he's positioned well, but for some reason a number of DPS and healers don't move to their pre-assigned groups, which I announced before both pulls, and they die in the second phase. Cue again the complaining, it sounds very similar to the first, though this time we had no fault in the matter.
We rez, I announce groups for a third time, and after the pull, six dps and two healers still manage to die in the second phase because they don't move.
We power through, and the remaining DPS is sufficient to beat the enrage timer.
The other tank tells me he is never tanking again, that he hates being yelled at. I agree, it sucks, especially by a mass of people who can individually completely slack off and still move through. I'll keep tanking, but it's because I'm mainly moving into flex and normal with the guild and LFR is a good way to help my bad luck shield RNG.
The simple matter is that there are more than enough tank classes, and Blizzard implementing two additional classes in DKs and Monks was a great move, but as long as you have 23/25 people in a raid able and willing to dump all over the tank, the emotional toll is going to keep out most people who can just as easily roll a DPS, wait in a long que, but not deal with the garbage that I went through last night.