A scenario like many others. Low level roulette, Basic Training Enemy Parties.

The party? A conjuror, a rogue, a marauder (new) and an arcanist.

The rogue runs out into the groups of enemies before the tank gets her bearings, pulling all the mobs on him and nearly dying. The marauder does her best to get aggro, but the rogue continues to pull.

The main enemy shows up and the rogue has all the enemies on him. The conjuror refuses to heal the rogue because, well, rogues make poor tanks. The marauder does her best to take control, and the duty ends.

The conjuror points out that rogues make poor tanks, and the rogue agrees saying they are DPS. The conjuror then asks why the rogue tanked if that's the case, and the rogue and arcanist state the tank is new so they wanted to help her.

The conjuror argues they are not helping, they are doing the tank's job while she watches.

The conjuror is called a number of names.

So I ask ... who was in the right? I'm curious to know.

Because a class that does another's job for whatever reason is silly. Giving the excuse they are doing it because the other class is new is stupid as well. If they are new, assist them in learning. Let them experience what they must do.