I suspect these numbskulls are thinking, "Look at those idiots, getting around our Perfectly Reasonable restrictions on smoking by using these e-cigs. Bastards! We gotta stop them!"
Doesn't exactly pass for adult-level cogitation, but that's what I suspect they're thinking.
E-cig vapor looks like analog cigarette smoke. Too difficult for enforcers to tell the difference. Liberals don't like the analogous suggestion to ban drinking water in public because it looks like vodka or gin.
But it is fun to poke the liberals anyway.