e-cigarettes still emit a smelly, visual byproduct. The proponents claim "It's not smoke—it's vapor!" Just wait until you're sitting next to an 80 year old nam vet on an airplane who insists on "vaping" because "hey, it's not smoking."
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).
Edit: speeling on my phone.