My take on it is this game isn't designed to require max efficiency. You won't fail your dungeon if the healer isn't dpsing.
I figure this stance is more to protect healers that aren't comfortable with DPSing than it is to encourage lazy behavior. That interview also mentions that the Cleric Stance change was to reduce the risk for healers that wanted to try DPSing as they wouldn't have to worry about being locked in when they need to heal.

I know for myself I was terrified to DPS when I first leveled WHM around 2.2. It was a slow process of me starting to DoT things during downtime then finally using Cleric as I got more comfortable with the role.