I actually had a duty finder WHM get so angry at a returner tank in Dusk Vigil that they actually left when the tank ignored their demands to mass pull. The tank was surprised when the healer dropped, and asked us if he'd done anything wrong. We assured him that he hadn't and to keep pulling at his own pace. We dps were both melee jobs anyhow, so there would have been no advantage to big pulls besides Holy, and without Thin Air that drains mp super fast.

The next healer was much more understanding.

Most people will be understanding. As you gain confidence with holding aggro and using your cooldowns effectively, you may find it easier to pull big packs together. But take it at your pace, don't let anyone force you.