When I heard of a smoking fetish, I was like "oh awesome, yes I have that". Turns out it's not an addiction, but sexual arousal from the image if someone smoking.
The base for capnolognia relies many variables. As with pretty much everything, it comes down the Madonna and The Whore; the smoker is a standardized, innocent, cute individual behaving in ways that are recognized as taboo, or it is captivation by a more salacious person, whose smoking characterizes their power and confidence. This fetish is heavily featured in femdom porn, as one can imagine.
Within gay culture, this fetish is often rooted in the image of masculinity.
Personally, I'm pretty sure everyone thinks smoking is sexy.
