"Willful defiance" is hardly a "relatively minor infraction" that rarely merits a suspension from school. Unchecked, it leads to a breakdown of classroom discipline, adversely affecting the majority of students who are there to learn.
School suspensions can be viewed in quite a different way than as a reward. As a former middle school dean who ran the referral room, I can say with some certainty that school suspensions are a tool to get parents involved in helping to curb defiant classroom behavior that eats into vital instruction time.
And anyone who has been in the Los Angeles Unified School District long enough knows that the resources needed to set up referral rooms in most schools will never be allocated. The inevitable outcome will be that out-of-classroom personnel will counsel a student and immediately send him or her back to the classroom, at which point the teacher's discipline will be permanently undercut.