I found this quote from Blessing of Kings: Warhammer Online: What to Play? to be a very good summary of the dilemma faced by healers (and to some extent tanks).
The thing about healing is that it is usually very powerful and scarce. And I don't *hate* playing a healer. So I could go healer, and my group or side would probably be more successful. Or I could go DPS, and my group or side would probably be less successful, but I would have more fun. But losing is not fun and winning is. So round and round in circles I go.