Not DPSing on a Healer when you don't need to heal is like stopping DPS as a Tank when you've gotten hate. Your job does not stop when you've accomplished your role. A tank could easily just spam flash and never do any DPS, and everyone would agree that they are a shitty tank because of it. A healer that does not DPS when they have spare time is a bad healer.

If you want to never DPS on healer (or defend those that don't), fine. Just don't pretend that they are not bad at their jobs because of it.

Being good at your job means using every tool at your disposal at the time when it is most effective to do so. Standing idly when you could be doing something productive is never good, regardless of your "playstyle" or comfortability.