"Heavy marijuana use in adolescence or early adulthood has been associated with a dismal set of life outcomes including poor school performance, higher dropout rates, increased welfare dependence, greater unemployment and lower life satisfaction."
Sounds like at least a partial recipe for a school shooter, no?
And I am a full advocate for legalization, but I'd prefer 25 over 18 or 21 as the age.
Link: https://www.apa.org/monitor/2015/11/marijuana-brain