If a healer is DPSing, I wouldn't call them lazy. Depending on the fight, they may be foolish, but foolish is not the same as lazy. A healer needs to gauge how much time they spend healing, and how much time they spend DPSing. If a healer is letting the group wipe because they're too focused on DPS, they've made a very poor decision, but at least they're spending their time doing something.

Lazy is a better descriptor for healers who, when no one needs healing, simply do nothing. There are a lot of 8-man fights in this game where a single healer is more than sufficient, and yet two are still required. It's not at all a bad idea for the second healer to go full DPS.