I never smoked. Aside from the health risks, which weren't quite as well-known when I was at an age when I might have started, there were a couple of other reasons why I never did:
1. My mother smoked, and the second-hand smoke burned my throat and made me gag. Whenever I have to be in a room with smokers (which, thanks to current smoking laws, is never anymore), my throat gets really sore. I'm happy to say that my mother smoked her last cigarette on New Year's Eve 1980, and hasn't smoked since.
2. When I was in high school, and EVERYONE else was starting to smoke, I felt so alienated from my peers, and despised them so much, that I didn't want to do anything that would lump me in with them. That included smoking, trying drugs, and cheating on tests. Not that I was a goody-two-shoes; I cut school all the time. But those were the things that it seemed like EVERYONE did, so those are the things I rejected. I had a best (only) friend, who was a bit of an outcast like myself, but she eventually joined in with the "punks" and started smoking and trying drugs. That was a huge disappointment, because I thought she prided herself on not being a herd animal. It was like, "Et tu, Brute?"
When I was in the Air Force, again, EVERYONE smoked. My boss sat defiantly under the "no smoking" sign, and smoked all day. If you complained about your roommate smoking, you'd get a talking-to about your attitude problems. I had a constant sore throat, which I now realize was from being around constant second-hand smoke. The doctors were always giving me antibiotics, because that was their answer to everything. Very weird.
Having said that, if people want to smoke in their own houses, I don't care. Of course, if my neighbor goes out on his patio and smokes, it comes right into my window and makes me gag, so I'd rather that he didn't. And if the person in the car in front of me lights up, it's the same thing. But as long as I don't have to smell it, I don't care.