Assuming that the intent of indoor smoking bans is to minimize the amount of smoke that is indoors, and assuming that e-cigarette use indoors is not causing an increase in illegal smoking indoors (why would it?), then I don't understand this specific concern.
Edit: speeling on my phone.
Not to be overly crude, but so does my ass after I eat to much mexican food. So do my burps, after shotgunning a bunch of vodka-redbulls. As for visual byproduct.. would it be better if it were invisible? My behavior after too many vodka-redbulls is far more of a public nuisance, yet they still let me drink those indoors (actually, I am not allow to drink them outdoors. Weird.)
Anyway, I have a few friends who use e-cigs. Can't say I notice it. My hypothesis here is that people primarily get bent out of shape over e-cigs because they feel that the users are "cheating", and nobody likes a cheater. That or they forget what somebody actually smoking is like.
It's about common courtesy.
The question isn't "can I burp in your face?", the question is "can I burp indoors?"
Smoking or vaporizing is something that people choose to do for extended periods of time, and doing so in an enclosed space, especially many people doing it at once, can fill air in that enclosed space with the byproducts, which may be harmful.
If people drank something that made them burp constantly, permeated the air with the smell of those burps, and that vapor was harmful, then absolutely that should not be allowed (beer does not quite count; you don't generally burp continuously while drinking it, though it may cause an occasional burp, and it doesn't cause a lingering, carcinogenic vapor to permeate the space).
I could also imagine that they could reduce the social pressure against smoking, as people would be seen happily puffing away on e-cigs which, from a distance, look an awful lot like regular cigarettes. Impressionable kids, people who have quit smoking but may be tempted to go back, etc. will now see smoking suddenly becoming socially acceptable again. Some people may see it and think that smoking is allowed wherever this is, and then light up a real cigarette.
There's a further sort of puritanical attitude that many people have towards smoking, I think due to the fact that it was so prevalent and so obnoxious for much of the 20th century. Much as some people have a puritanical attitude about drinking (and we still have ridiculous laws stemming from that), that attitude may persist about smoking even if e-cigs turn out to be much less obnoxious than cigarettes.
You have to remember, there are plenty of people who were non-smokers during the middle of the 20th century, when you couldn't go to a bar that wasn't saturated in smoke, where you had to breathe in secondhand smoke almost everywhere (even in the non-smoking section of restaurants, it would still waft over from the smoking section), where if you lent something to a smoker it would come back reeking of smoke. The idea of losing ground on the fight that was just recently won, of not allowing it in most indoor public places, makes non-smokers fairly anxious.
Now, if it can be demonstrated that secondhand vapor from e-cigs is perfectly safe, and that it doesn't permeate the air with the same foul smell, then maybe their introduction would be welcomed.
After all of the damage we've done over the years by rapidly accepting new technologies that wind up poisoning the air (see, for example, secondhand smoke, leaded gasoline, diacetyl, asbestos, the Great Smog of '52 and the continuing smog problems in Beijing today), we need to be less willing to simply assume that releasing something into the air we all breathe is perfectly safe, and instead only allow it once it has been demonstrated to be safe.
As far as I can tell, e-cigs only started becoming popular in the last few years. While I'm fine with people using them in their own homes or outdoors (since there's a certain level of concentration below which it's not worth worrying about anything), I'd be very skeptical of accepting them in establishments in which smoking is not allowed without further study.
All I'm poking at are what I do perceive to be irrational arguments against them.
Arguments like:
> "Impressionable kids"
Ban real cigarettes in movies and outdoors then.
> "people who have quit smoking but may be tempted to go back"
No special considerations like this are afforded to recovering alcoholics.
> "The idea of losing ground on the fight that was just recently won, of not allowing it in most indoor public places, makes non-smokers fairly anxious."
Their anxiety is irrational, indoor smoking is not making a comeback. If second hand e-cig vapor is a concern, it is an independent concern.
However, before I'm willing to support e-cigs in indoor public places, I would like good evidence from independent third parties about the safety of secondhand e-cig vapor. The problem is that there's a catch-22; this kind of information is hard to obtain without them being popular enough and acceptable enough to reach the same numbers of people in indoor places at approximately the same concentration as smokers, and for long enough for long-term affects like cancer and heart disease to become distinguishable. I'm not really sure the best way to address that kind of problem; of safely studying something that has the potential to be harmful in the long term, but also has the potential to displace something even more harmful.