The arguments aren't nearly as deluded as the underlying notion that "breathing air is worse for you than vaping," primarily because there's a huge lack of research. Beyond that, there are certain known risks associated with vaping -- things that many people aren't that educated about.
Many juice manufacturers don't really care about diketones and most people aren't aware that burning your e-liquid can produce harmful, carcinogenic aldehydes. When I'm walking around in the street I'm FULLY confident I'm not inhaling 10x my recommended daily dose of diacetyl/AP, whereas when I'm vaping it's very possible that I am.
So the bottom line is risk management/avoidance, right? You quit smoking because it's a known risk (agreeably pretty high in terms of risk), and instead you picked up vaping. Vaping is pretty much an unknown in terms of how dangerous it could be, but we can pretty safely assume that it carries less risk than smoking. On the complete opposite end of the risk scale is "breathing air," something that people have been doing for hundreds of years, both with and without carcinogens/pollution. (In fact, despite steadily/exponentially rising population/pollution/etc., average life expectancy has literally doubled since the 1920's.)
Where do you get the evidence to make any rational, logical, scientific claims that vaping is as safe (or safer) than breathing regular air? Is it just common sense?
Well, there's no formaldehyde for one thing, since I don't burn my wicks, but in any dwelling with carpet, there is a background level of formaldehyde, and in some places, a great deal more than mere background. In vaping, there is nothing burning (if one is doing it correctly!), but the products of every kind of pyrolysis are in the air everywhere -- cars, trucks, the neighbor's trash fire, industry, etc. We've gotten used to the idea of cars and trucks, so they've become somewhat invisible, but there is definitely burning going on, and burning any products of dead dinosaurs is very far from non-toxic.
That's just for starters, right off the top of my head. I seldom use the "common sense" argument for anything, because there is nothing so uncommon as 'common sense,' nowadays. But I really don't need to go find "evidence" of all the other nastiness present in the air that a large majority breathes on a daily basis; the vast majority in the US live within 50-100 miles of some kind of city, where the pyrolysis products are GOING TO BE present, there is no escaping it.
The *only* real potential risks with vaping, for *most* people, are going to be found in the flavors, simply because we don't yet know what regular, frequent, direct inhalation of those flavors will do -- maybe nothing, maybe lots of bad -- we don't know yet. But the other components of e-cig vapor, for the vast majority of people, are non-toxic -- they may have sensitivity issues, as I do with VG, or as others do with PG, but that doesn't really constitute a toxin; I suppose it's more on the order of an allergen, it causes an unpleasant response despite the non-toxic nature of the substance.
I think the real point of the whole thing is, there's really nothing GENERALLY TOXIC in vapor -- saving those nasty diketones -- while there is a great deal of GENERALLY TOXIC out there in the air -- if most of us are managing to breathe that air without ill effect, then it just stands to reason that vaping will not cause ill effect either. I did not say 'common sense,' I applied logic.
Andria