I think SE didnt intend for healers DPS to be considered into raid dmg, but, i do think they intended healers to throw out damage occasionally (by design of the job, not encounter) just for "fun".
(To clarify, I know, and agree with, that yoshida said they dont take healer DPS into consideration for raids)
The reason healers DPS so often, is due to bosses auto attacks doing so little in damage.
But the irony, is that the reason bosses auto attacks do so little in damage, is due to healers healing so little on a basic GCD heal.
If a boss bring a tank to low HP, the healer either has to use emergency oGCDs, or spams cure/cure2 until they are full hp. Which if the bosses auto attacks were still like cleaves in damage, means our current healers wouldnt be capable of keeping up with the damage. they woudl run out of oGCD/emergency options.
So what is the answer? Stronger heals? Then there is almost no difference between a normal auto and a tank buster, since both bring tanks to really low HP. And are treated nearly the same.
It would get the WoW treatment, where HP ping pongs from low hp to full hp, back and forth. Healers get more emergency heals, and tanks get more mitigation to upkeep.
which seems to be the opposite of what SE wants to do.
The ONLY reason I can think of, is that SE does want both tanks, and more so healers, to throw out occasional DPS. Healers can ONLY throw out GCD DPS, if a tanks HP isnt ping ponging around.
The only way to do that, is to lower auto attack dmg of bosses, and lower healing potencies of healers.
OR to give healers a ton of strong/useful oGCD DPS to weave inbetween.
which, lets be honest, is perfectly fine, and not broken. I think SE thinks this would be broken, and make healers near DPS levels of damage, but if they cant afford to spend GCDs on nukes, you just cut their DPS in half (or more) and in solo content, healers can output DPS on levels of a tank in DPS stance, making them far more enjoyable in solo content.
But anyways, this is why I feel SE did think healers WOULD throw out damage spells, but at the same time, why they dont calculate it into the amount of DPS needed to win a fight.