Undercover thugs in US high schools pressure vulnerable students to buy drugs to sell to them, in order to prosecute them.

Undercover infiltration is legitimate as a way to catch people who regularly commit crimes of their own volition. Selling marijuana to minors should perhaps be a crime even when it is legalized in general, but teenagers who do this occasionally when pressured by other teenagers are the wrong targets.

Juvenile punishment could perhaps be useful for teaching them to change course in life, if they had a second chance. However, expelling these students from school is a punishment for life, denying them that second chance.