As a smoker myself let me clue you in on a couple of things,
Firstly Nicotine is as addictive as cocaine, and your friends that jus quit "cold turkey" I would BET they were closet smokers for a good long time after, please its like saying Drug Addicts aren't addicted (though I agree these are addictions of CHOICE if you chose NOT to do it in the first place, then you DO NOT become addicted ), like a drug addict, a closet smoker can and will HIDE their addiction from even the people who live with them, and become quite good at it, ever wonder how a Meth Addicted Mom can hide it from their spouses and kids ? Same idea.
Look you chose NO to smoke, that's great, really, but I am NOT a criminal (cigrettes are still legal ) nor am I the greatest contributor to Global Warming or air Pollution, and yes despite what you might think, Nicotine is an ADDICTIVE DRUG, both physical and psychological, the people who say they have quit with NO DT's from this are LIARS or damn good actors (worthy of Academy Awards I daresay ) Most of us who have tried and failed or succeeded will tell you the same thing, that's why the aids are popular, they take the edge off, would you suggest a coke addict just QUIT "cold turkey ".
Its like anything else, if you haven't experienced it for yourself, you cannot KNOW, and you know what if you use that attitude with your friends, they will NOT tell you the truth of how they are feeling at that moment.
We do get that it isn't good for us, we know that, just as an alcoholic KNOWS that drinking could KILL them or a Drug Addict knows their addiction could KILL them, we know it.
You've already kicked us out of society, you've already stigmatized and ostrasized us, be happy with that, and if we chose to continue then just be happy we are not in your space.