I switched to e-cigarettes and I cough less, have a better sense of smell and taste, and I feel healthier, what's the problem?

Just because you feel better doesn't mean that you are "healthier". We don't know the long term effects from vaping yet. It certainly will NOT be the same as with traditional cigarettes but e-cigarettes will have their own disease profile. 

Part of the problem is with the flavors--while they may be GRAS for ingestion, most have not been tested for inhalation. 
e.g.  Lawsuit Filed Against Butter