When the product should not be used according to Health Canada - not so benign - how many men have been told not to use alcohol if they wanted to have children ? How many people have died after standing next to a person drinking a beer from second hand smoke ? 
No need to compare marijuana to alcohol or tobacco - it has its own  problems believe me - psychotic breaks, addiction, reproductive toxicity, carcinogenic second hand smoke exposure for the non-user, risk of cognitive damage in the young, increased risk of suicide and the list goes on.

Cannabis should not be used if you:

are under the age of 25
are allergic to any cannabinoid or to smoke
have serious liver, kidney, heart or lung disease
have a personal or family history of serious mental disorders such as schizophrenia, psychosis, depression, or bipolar disorder
are pregnant, are planning to get pregnant, or are breast-feeding
are a man who wishes to start a family
have a history of alcohol or drug abuse or substance depende