Well. The idea that because most criminals used marijuana at some point in their lives caused their criminal behavior is a flawed argument from the outset.
I can say with utmost confidence that 99.9% of convicted felons ate bread as a youth. Therefore, the bread caused their criminality. Just throw it out!
The facts are, humans love mood-altering drugs. Human teens have been drinking ethanol for 5,000 years or so, and no law is going to change that behavior. (Nanny state, conservative friends?) I'm not sure about marijuana, but it is a milder drug, which doesn't cause aggressive tendencies like liquor, so, shrug.