How do you know that it is not about safety or health? Do you have any study that says they are safe? It is amazing how many delusions a little marketing can create.
But the reason cigarettes are banned is because they affect other people.
American rules/regulations aren't built around the concept of proving something is safe. Tobacco is different from the norm because of how much evidence exists to prove its harm
It is at least plausible that the risks of e-cig users around you is negligible, especially compared to your dry-cleaned suit, the air quality of the airplane you flew on, the radon in your house, etc.
In that context, don't you find it curious that the negative reaction is so strong against the idea that people who enjoy a nicotene buzz can have their cake and eat it, too?
To me it doesn't look like caution. It looks like a bluenose impulse to control people for what is likely to be no good reason, and is well below the threshold for regulating access to other psychoactive substances.
Now if people really are motivated only by protecting other people from a significant new source of risk, then I'm sorry. But, man, it sure looks like e-cigs are a touchstone for revealing prohibitionists.