Zero tolerance is a blanket policy used widely in America wherein everyone is punished for the same "crime" regardless of individual culpability, extenuating circumstances, or history.
By simply claiming "zero tolerance", these people, whose jobs are to uphold morals, are able to instead shirk their duties; additionally, many people in positions of power use this policy to absolve themselves of its consequences.
There are cases where children have died due to not having immediate access to a rescue inhaler because it is a drug, and all drugs are treated the same. There are other cases where children's future has been put into jeopardy for things as simple as plastic knives or holding their hand in the shape of a gun. These kids are punished the same as kids that bring handguns to school!