"Why can't zero tolerance use less drastic punishments?"
You seem not to have read my post. The reason it exists is to allow the arbitrary destruction of kids lives, preferentially as a weapon against minorities, undesirables, the poor, often all of the above. You're treating the primary purpose of that feature as if its a bug. Like asking why the "rm" command takes the drastic effect of deleting files.
For example, one reason why it might exist is so if a teacher gets called a bitch, the cops would laugh at a teacher who tried to report that as assault, but if the teacher can label a girl as a drug dealer and get her expelled and prevent her from graduating or getting on the middle class treadmill in general, because of the girl's monthly cycle and some advil in her purse, well, we'll see who's the dominant primate and who gets the last laugh in that argument. Its NOT a bug its an intentionally inhumane feature, correctly implemented.
Its possible to do a really efficient and effective job of being evil. I don't really know how to rephrase it more clearly? Its like the anti-google motto or something?