The Christian perspective that marijuana (since it is a "drug") is inherently evil probably comes from this quote:
1 Corinthians 6:19-20
Or do you not know that your body is a temple of the Holy Spirit within you, whom you have from God? You are not your own, for you were bought with a price. So glorify God in your body.
Essentially, anything that clouds the mind or harms your body does not glorify God and is an attack on God.