The Role of Melee Combatants in a Group

[Tal]

I'd say that's part of it, but the other main point was situational awareness.  If not all mobs are accounted for in some way (be it taunting, sap, polymorph, etc.) then they'll end up attacking the healer the second he/she tries to cast even the smallest of heals.  Basically, people need to have a plan for engaging the number of things they need to.  If not, the first healing spell paints a big red bullseye on the caster.  :)

Exactly. And this is why just about every group could use a secondary tank to assist with gaining the attention of mobs.

But even in upper level instances, doesn't the party have some way to lock down (so to speak) the mobs so that they don't go butcher the healers when they cast?  If not, then perhaps that's one reason why there are so few Priest players around.   ;)

Sure. They bring a good warrior along. ;) Additionally they should have a secondary tank in the form of a battle stance warrior or a pally who knows how to gain aggro with a combination of crusader strikes, holy strike, fist of justice, or judicious use of seals. :) A rogue can also attain this but really should very rarely be called upon to act as a tank. Much of a group's success really centers around composition, communication and setting up a good battleground prior to engaging. Bad pulls do happen though and the group needs to know when to cut and run. This usually means leaving the tank to die however and the group (and to a degree the tank) has to be ready to do so. I usually caution a group that I'm the tank for by saying "If I say run. Book it because I'm dropping fast!" :D