I don't think the problems can be laid down at just one class or roles door. I feel for you if you've lost the will to live due to fail tanks but the action of some can make the good tanks think why bother.
Tanks at lower levels are learning the game and speaking from experience of picking up tanking as I go along there are a lot of crap we have to put up with.
I've leveled upto 45 via the LFG system and done pretty much all the instances availible to me along the way, and I've come across various players of different skills and abilities.
The ones that annoy me the most is the fully heirloomed I'm leet player who talks about how he managed kingslayer on his main (probably under the top level buff) and how everyone should bow to his skillz. This player is usually one of those WotLK players who has been carried to content and gear they wouldn't ever see if skill was required.
Instead of me pulling mobs in packs they pull and expect me to pick up the mobs running all over as they run in different directions, then blame me for them having agro when I haven't even hit the mob yet.
Those who stand in los when I'm pulling mobs outside of a room.
The warriors who charge in whilst I'm positioning mobs.
Players using knockback effects and pulling the whole room, about a second after my AoE agro abilities have just gone onto cooldown.
Players not knowing what role they are playing, a druid going from Kitty to Bear and taunting mobs off me for no reason.
Players using fear on securely tanked mobs.
The list of fail is endless.
You think you've seen it all but every LFG throws up something new.
I can deal with all the above, and just nuckle down and get on with it but what I can't stand is idiots who revert to abuse.
Omg wipe party rofl, noobs coming from the warrior who chain pulled multiple packs in DM north because he had no awareness of his surroundings. Then proceeds to complain because we are position the Captain away from the end of the hallway so the fears don't end up making players run into the mobs into the next room. Your runining my dps by moving him /facepalm.