Is smoking a sin? If not, why should Christians not smoke?

1 Corinthians 6:12 - All things are lawful for me, but all things are not helpful. All things are lawful for me, but I will not be brought under the power of any. 1 Corinthians 6:19-20 - 19 Or do you not know that your body is the temple of the Holy Spirit who is in you, whom you have…