MMO's have been out a long time.

This is still a problem.

Shut up, heal the person and try to finish the dungeon/whatever, and move on. Unless the person is in your FC or a regular in your groups, this will not have ANY real impact on them as, chance are, the next healer will just be all 'Oh hey, an asshat, eh, bads will be bads'

Your job is to keep things alive, don't stop doing that because some guy on the internet made you sad.