Healing doesn't get you as much contribution. It might generate hate, sure, but I've healed and I've DD'd entire bosses, DD wins every time.

Doesn't help when I get chased by all of the elite mobs because noone will take them off me either.

Personally I keep healing the tank every so often, but I risk losing my Gold medal when I do. (Cancer no heals: Gold 9/10 times, Cancer half healing tank: Silver or bronze).

In a party htough, hell yes, Medica = Insta-gold if everyone has got a good bit of hate spread around. Just not everyone joins, or can join (DF wait) a party.