Same thing everyone's said. When I see a healer not DPSing (in levelling dungeons) I'll kindly ask if they're aware of what Cleric Stance does. I'm giving the benefit of the doubt.
Most of the times they don't answer, though. At that point I just let them be mediocre and go my way silently. As others have said, no point in engaging in an argument with someone who will likely not bulge. That said, my approach also touches on the possibility that they may be true newbies and they'll be open to advice, which is the best case scenario.
I don't really bother in lvl 60 roulettes, though.
