You're believing the propaganda, zero-tolerance was put there because priciples and teachers are to lazy to do their jobs and want a one style solution to all problem, which never works.
Zero-tolerance rules are akin to sentencing a starving man to life in prison for stealing a loaf of bread.
It depends on the seriousness of what they're having for zero-tolerance. If a kid brings drugs to sell at school or is involved in a gang fight or gang violence --- just get him out. I think schools should be for the kids who are motivated to learn, who have some clue why they are there. Kids there to disrupt the learning of others should leave.