"Standing there doing nothing". Hmm, so they're not even healing either? And a healer necessarily doesn't have to DPS. They're more focused on keeping everyone alive rather than DPS'ing. The only time a healer should DPS is if the healer is confident in the tank and party members not dying. There was a thread on this concerning healers dps'ing.
https://forum.square-enix.com/ffxiv/...-Healer-Damage
My reply was - "I don't mind it when healers do damage. The main point of this all is when these "Healer's" think they are a DPS. They spend more time trying to DPS than healing which results in people dying which then causes a wipe. Iv'e seen it happen, healer's get into DPS'ing to much and don't heal and people die. Which causes of course, longer runs."
As for Healers intentionally not DPS'ing = rudeness? To me, no. They are healer's. The time that you will save from running the dungeon is very miniscule if a healer DPS's. So no, no one has to "Pick up the slack" for the healer.