It depends maybe on the school and the type of student. If you live in an area of high gang activity, it's best if there is zero tolerance so the gangs are out on the street or in jails and prisons where they belong --- some of these kids don't belong in school at all. If a kid thinks school is where they go to deal drugs or fight --- then they have no good reason to be there and ruin the other kids' chance at an education.
Zero-tolerance rules are akin to sentencing a starving man to life in prison for stealing a loaf of bread.