Your thread title suggests there arent enough healers.
But there are.
The real problem is more like "How to get people to ´become good healers".
Also, as an avid dps healer myself, I'm not sure I like this suggestion. It takes away a challenge/risk some of us like.
And I bet you, some are still gonna refuse it as a matter of principle. And some are still gonna be like "But, but...the tank could miraculously get one-shotted and die while I'm in the middle of casting Stone II for 2 seconds"
The people who would dps more without cleric stance are the people who would eventually start dpsing anyway once they feel more comfortable.
Only difference I expect here is that they might be inclined to start dpsing sooner because the risk/penalty of cleric stance is gone.