By the time you reach secondary school (high-school) you start to realize that everyone from your parents to your church to your school to your government has been lying to you, at least in some part. You start to distrust authority and the government and don't believe them even when they are telling the truth. If authority says marujuana has "no medical use and a highest potential for addiction" and you know that is not true, maybe they are lying about vaccines being safe? If they lied to you about masturbation, maybe they lied to you about STDs? If the authorities continue to lie, the citizens will continue to not believe anything they say.