My dad used to say the exact same thing, until he lost his job his family, and his life. He used to pretend that he was "functioning", and that his drug use wasn't a problem. This is a classic example of someone who we will read about losing their job and life in 10 years or less.

The only bit I will agree with is that addiction is not caused by the drug itself, and is typically the result of childhood trauma. With that drug use is not a solution for dealing with that trauma, dealing with that trauma directly through therapy and mediation is a much better solution.