The question arises from the fact that in this game, it's ridiculously easy to get away from people trying to kill you, and coupled with healer CC and spam heals, it's impossible to kill a competent healer unless they screw up and basically hand you a kill.
It's like trying to kill a healer in WoW, but worse, because they're also the CC machines AND they have a low cooldown blink. The only abilities that inhibit their heals last for no more than 1.5 seconds(read: Thorn's 1) and you can't kill them during a stun or root because damage breaks the CC and they'll teleport off as soon as they're out. I'm not talking about stupid healers that don't know what they're doing and let you beat on their face. I'm talking about blood priests that win 3 on 1's.