I'd also feel better about it if I knew that smokers were free to quit whenever they wanted. Unfortunately, most smokers are addicted. 70% of smokers would like to quit, but are unable to do so. (Last time we discussed this issue, I posted a link to this research).
Huh? Smokers can quit whenever they want to. They decide that the benefits of smoking simply outweigh the detriments. Some of those benefits and detriments of course include the physiological effects of smoking or not smoking. That's really no different than most other human activities:
* Eating
* Sex
* Sports
* Driving
* Scuba
* Sky-diving
* Breathing!
All of these things have some level of physiological effect that can be either good or bad associated with them.
I decide to eat ice cream, even though I know it's bad for me, because I believe the reward (yumminess) outweighs the risk (obesity, heart attack, etc.). Smoking is fundamentally no different.
To hide human responsibility and freedom under a veil of "clinical addition" is really missing the point: we all choose to live life in the way that we believe will bring us the most happiness. Smokers smoke. The obese eat ice cream. Adrenaline junkies jump out of planes. And we all breathe.