I think the main concern here is ones physical health, and what smoking leads to, such as cancer, lung and breathing problems, birth defects, and much more. Any thing that alters the mind or mood, and can become an addiction which cigarettes are, is sin because you are a slave to whom you obey!
You are destroying the holy temple of God, its very unhealthy for you and those around you, but any addiction such as food, caffeine, alcohol, drugs, plus all the addictions of the flesh such as porn watchings, TV and sports addiction are sin also.
Rom 6:16 Do you not know that to whom you yield yourselves as slaves for obedience, you are slaves to him whom you obey; whether it is of sin to death, or of obedience to righteousness.
Rom 6:17 But thanks be to our God that you were the slaves of sin, but you have obeyed from the heart that form of doctrine to which you were delivered.
God warns that if you destroy your holy temple He will destroy you, which to me are strong words from God, no to be taken lightly.
1Co 3:16 Do you not know that you are a temple of God, and that the Spirit of God dwells in you?
1Co 3:17 If anyone defiles the temple of God, God shall destroy him. For the temple of God is holy, which you are.
I just don't see smoking in moderation as being OK, as to its addictive qualities, so its good not even to start it or try it.
Most are unwilling to give up anything for God especially thier smoking, and other addictions that hamper thier relationship with God, and leave them in a lukewarm state, still in bondage to thier lusts and passions.
If repentance and faith were preached correctly right from the start, then this wouldn't be in question, as a truly repentant heart who has actually crucified thier flesh with Christ as commanded, will have no problem forsaking thier smoking addictions along with porn, adultery, worldliness, and drunkenness, etc..
Some will also say it doesnt matter how you live your life, as long as you accepted Jesus as your savior, then smoking and other addictive behaviors are not good or healthy, but have no influence on your salvation!
But I think the above scriptures make it clear how we are to live on the narrow road, and also to be a strong example for the lost who love thier smoking, porn, and Drug addictions, lets come out from among her, be seperate, guard the heart from all and any addictive habits, and count the cost of living right and healthy before our God who is a consuming fire!