Healers that don't want to DPS are like DPSes who refuse to move out of AoEs.

[Onyxia]

It's bloody painful when I can visually see how much slower their targets are dying compared to mine

And? They do damage? Yes. Mobs die? Die. Who say that they need to improve? I am sure they like their play style and feel themselves comfortable.

Also, one day ago I saw summoner who did not use aetherflow and bane, energy drain, etc. He only spammed ruin on one target... Could I blame him? Of course not. We still beat the dungeon. Who cares that we spent 40 minutes on this duty. Healer was not DPSing too, of course.