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

[Taika]

There is a 4th option, that they simply do not find DPSing fun, and that is why they chose to heal.

If you don't find a job, in it's entirety, fun, don't play it. If I don't like pets, I don't pick SMN or SCH. If I don't like to support, I don't pick BRD or MCH.

It's not any more acceptable for a healer to ignore the useful abilities in their toolkit than it is for any other job. Healers shouldn't get a free pass just because they're called healers. They should be expected to participate just as much as the rest of their team mates and they should be expected to use their abilities in a way that's as useful as possible to their group just like everyone else in the party.