Argument has never been about DPS, it's about idling.
It's just that doing DPS is the only option after the healing is taken care of.
Pretty much everyone who's actually on that side of the argument would agree, as long as you're attempting to cast a beneficial skill every time the global cooldown comes up, you're fine.
It all has to do with fairness, if every other member of the party is expected to be using a skill every time the global cooldown comes up, the Healer should as well.
Remember the ABCs, always be casting.
If the healer is in a situation where every Global cooldown needs to be a heal, that's fine as well.
It's situations where stuff like this...
... Comes up where people are getting upset.