2 points:
1. Just because socially-accepted alcohol is bad for your health doesn’t mean marijuana is somehow good for your health. Both alcohol and marijuana are bad for your health.
2. Studies in recent years have shown correlation between chronic marijuana use and increased prevalence of anxiety, paranoia, and schizophrenia. Correlation does not necessarily equal causation, but we do society a disservice if we ignore and hide this correlation. The risk of brain damage should be a reason why many people (pilots, surgeons, truck drivers, police, etc) should avoid marijuana.