Are healers lazy or do some really live by "I only heal"?

[Trashy]

but I don't think a healer is bad for not DPSing. And I think it's really pitiful when a party really -needs- a healer's DPS in order to kill things.

Maybe not bad, per se, but they aren't good. A good BLM uses Apocatastasis. A good SMN uses Virus and Eye for an Eye, a good BRD uses his songs, a good MCH uses Promotion, a good WAR uses Storm's Path, a good PLD uses Cover, Divine Veil, and Clemency, a good NIN uses Shadewalker, Smoke Screen and Goad, a good MNK uses Mantra, and a good healer DPSes.

If you're failing at your own role, you're bad. A SMN not using Dreadwyrm stance is bad, a WHM letting a tank die is bad, a PLD not using cooldowns well is bad. But if a player isn't using all the tools they can to help their group, then they definitely aren't good, even if that help falls outside their Holy Trinity role.

[AeraLure]

a WHM letting a tank die is bad

Obviously it's not that straightforward. I take it personally when anyone dies, but some tanks really make an effort.