You would think that after a century, the realization would dawn that marijuana is harmless to most everyone. There isn't a reputable physician who can answer up to the reality that even those who smoke it are actually rejuvenating their lungs. IF they give it a break now and again. Which most do.
Probably the most prevalent "heavy smokers" smoke about a bowl full after they shower up after work. And that's that. Maybe TWO bowls smoked on Saturdays, GASP!
So, what's the cost in the long run?