The way I view it is that you are all a team and have a goal, your primary role is to heal but you are given DPS capabilities. A DPS's primary role is to DPS but is given support capabilities etc. Everyone should do what they can to complete their goal as effectively as possible. If your goal is to kill a boss, DPSing the boss helps - so do it.

The only reason players view healers who don't DPS as lazy is because healing in this game is very lightly tuned - resulting in non-DPSing healers to stand idle and do nothing. My pet, as you mentioned, can solo heal trash and bosses almost fully in expert dungeons. My pet has roughly 200 potency heals and is upped to 280 for 20s every minute. That's on average about 225 potency heals every 3 seconds. Regen, conversely, will do 150 potency every 3 seconds - except when Divine Sealed which bumps that to 195 for 15s - so 160 potency every 3 seconds. While less, that still means that regen alone should keep your tank alive - with only minimal needs to pop out of cleric and cast a cure. That means that over the course of a pull, you may cast 2-5 healing spells which works out to maybe 16% of the pull. That leaves 84% of the pull where you are doing nothing, but watching. That's a lot of time that you can get out some very significant DPS.