My biggest problem when it comes to this are the healers who keep healing the problematic damage-dealers. Most of the time I ask them not to heal the damage-dealers when they do that, and to let them die, they reply with something like, "ugh, can we just get through this dungeon?" and keep on healing. At that point I just tell them they need to find another tank, and leave the duty.

It was like that in FFXI too, I've noticed - this kind of "it's fine to suffer through anything as long as you get the job done" mentality. It's poison.