What is wrong with smoking?
Perhaps I should turn the question around and ask "What is right about smoking?" After all, it is an expensive habit that is known to cause damage to the body of the smoker. So what benefit does smoking give that should cause a Christian to consider it?
Tobacco is considered to be highly addictive. Recent studies show that it affects the body in two ways. First, the chemicals in tobacco stimulate the pleasure center of the brain making the smoker feel good even while they are filling their lungs with smoke, which causes non-smokers to cough heavily in attempts to clear their lungs. Second, the brain has a natural limiter on the extent good feelings last, but nicotine blocks the "off" switch for up to an hour after smoking. Hence, the smoker continues to receive pleasurable feels for an extended period of time.
The apostle Paul declared, "All things are lawful for me, but not all things are profitable. All things are lawful for me, but I will not be mastered by anything" (I Corinthians 6:12). Even if something is wrong in and of itself, it is not good for a Christian if it holds no benefit for the Christian. It can be harmful to the Christian if it rules a Christian's thoughts. Paul illustrates his point by using food, drink, or sex as ways a Christian can lose his focus on spiritual things and become concerned with worldly matters.
Consider that tobacco holds such a strong sway over the smoker that he will spend his family's food money to purchase a pack of cigarettes. I have had smokers tell me they have no money for food, clothing, or rent while I see a pack of cigarettes bulging in their shirt pocket. Tell me who is being dominated? Peter commanded, "Beloved, I beg you as sojourners and pilgrims, abstain from fleshly lusts which war against the soul" (I Peter 2:11).
Paul also warned against Christians causing harm to their bodies. "Do you not know that you are the temple of God and that the Spirit of God dwells in you? If anyone defiles the temple of God, God will destroy him. For the temple of God is holy, which temple you are" (I Corinthians 3:16-17). Defiling God's temple covers a range of things from using the body to engage in sinful behavior to damaging the body so that is no longer fit for useful service.
Since there are a large number of harms and no benefits, Christians should not engage in using tobacco products.