Yes, but for better or worse[0], smoking is considered common good. Here we're talking about replacing smoking, which is clearly very harmful, by e-cigarettes, which are maybe somewhat but insignificantly harmful. The cost-benefit analysis of that alone[1] should convince everyone to cheerfully advocate for them.

In the course of this discussion thread, we've jumped from the danger of e-cig vapor (which is nil) to the danger of pure nicotine (which is also nil) and now we're talking about pollution. Can't we just agree that those are three separate issues (two of which are non-issues, and third isn't really discussed by people right now)? So far everything is showing that e-cigs are a neglible hazard to smokers and their surroundings. We should be happy we've found a good alternative for the decades-old problem, instead of trying to destroy it by overblowing its negative effects by orders of magnitude.

[0] - Googling just now, I found that there are reasons for considering cigarette smoke an air pollution - http://epi.yale.edu/the-metric/considering-smoking-air-pollu...

[1] - I haven't seen any analysis about potential of e-cigarette smoke becoming a significant pollutant; it most likely won't be in terms of particulate matter, but maybe the smoke itself is bad for atmosphere. I don't know. But even if, that's a discussion about environmental impact (and a one that no one is having right now), not about direct health effects.