It's actually good news. In the seventies we were told that smoking one joint was the same as smoking 6 cigarettes.
Most people who smoke dope don't smoke it all day - everyday. You can't stay loaded 24/7 (not and keep a decent job LOL). The people that I know smoke occasionally - usually on the weekends. So I doubt that the lung cancer scare is a valid point.
I know people that have gotten lung cancer who have never smoked. The writer Calvin Trillin's wife was one of them.
Kathleen