I don't tank, but I do a bit of healing on the side. If I were to tank (Duty Finder), and I ran across a healer that wasn't doing any damage, I'd politely ask them if they were ok, and reassure them that I know what I'm doing and I should be able to provide them with ample windows to do damage and still keep the team afloat. Maybe even offer to move a bit slow at first so they can get their feet wet and their confidence up.

If they were jerks about it, or I figure out that they're just lazy, then I'm pulling half the dungeon. If they are going to sit there and do nothing but heal out of spite or sloth, then I'm going to give them some healing to do. I'm the tank. I dictate the initial pace, and can use it as a motivational weapon. Granted, they can just not heal me and then I have to deal with that whole issue. Still, tank. Instaqueue.

Now, if this is a Party Finder affair, then I would have advertised ahead of time that if you don't DPS, I'm putting you to the curb.

I will agree that I don't see any of the roles get as much grief about damage output than healers. Maybe because it is the only role where damage is 100% separated from their core duty.