Personally, I don't consider it a healer's job to dps, but I do consider it boring to stand around as a healer when there's not much to heal outside of throwing out a regen to the tank here and there. Plus, a little extra dps speeds things up and there's no wrong in that. If I'm not on healer, I won't complain if the healer doesn't dps because I can understand there's situations where they might not feel comfortable, and those situations aren't always apparent to the rest of us.