Healers that don't want to DPS are like DPSes who refuse to move out of AoEs.

[Kitfox]

It's honestly not even an argument. Healers heal, the DPS side of it is an optional optimal way they can help due to the potency of it. It will never be mandatory or "bad healing" to not DPS as healer. Maybe inferior healer DPS, but not inferior healing.

Your argument is even worse:
"It's not bad tanking, just inferior CD usage!" - Tank that doesn't want to use CDs.
"It's not bad MNK DPS, just inferior positionals!" - MNK that doesn't want to use positionals.
"It's not bad DRG DPS, just inferior combos!" - DRG that doesn't want to use Blood of the Dragon.
"It's not bad SMN DPS, just inferior DoTs!" - SMN that doesn't want to use DoTs.
"It's not bad BLM DPS, just inferior use of fire magic!" - Ice mage.
"It's not bad support, just inferior TP/MP regeneration!" - BRD/MCH that doesn't use songs/turret.

But hey, it's all optional optimization, right?