Don't make light of cannabis, it is a drug and like all drugs has side effects. Even moderate use can seriously retard and arrest brain development in teenagers and it can accelerate the onset of schizophrenia in those who are at risk. It's also been associated with lack of motivation, focus, bipolar disorder, depression, and anxiety among a host of other issues later in life.
Fully grown adults should be able to choose to do what they want but people who peddle drugs to children deserve nothing short of the death penalty.