In my personal perspective I considered smoking as a sin as it is related as form of vice.Vice is define as moral depravity or corruption,a moral failing or bad habit.All sins indicated in galatians 5:19-21 doesn't mention smoking but there's a word says and the like that something related to.It says "The act of the flesh are obvious: sexual immorality, impurity and debauchery,idolatry and witchcraft,hatred,discord,jealousy,fits of rage,selfish ambition,dissensions,factions and envy,drunkenness,orgies, and the like.I warn you, as I did before,that those who live like this will not inherit the kingdom of God.