Part of that learning process is that the consequences are proportional to the action. If your premise holds true, the poor boy will think vandalism will get him the chair.
And sometimes life isn't all that fair. Just because a worse offense carries the same punishment, doesn't mean that the lesser offense is disproportionally punished . The point is, the kid deserves some sort of punishment.
I think that too often administrators hide behind cookie-cutter school rules and zero-tolerance policies, without any care for true justice. And too often, parents of the worst brats constantly make excuses for their little imps, and their precious little spawn never learn to function in the real world, except to hate those who disagree with them.
Look, if this were my kid, he'd not only be lectured to death, but IF I really thought the punishment had long-term consequences that were truly hurtful, I'd talk to the administrator privately, while not telling my kid, so as to scared the * of him and let him really think about his stupidity. IF it became a matter of fighting the system publicly, I wouldn't be making excuses for my child, but rather I would explain to him that while there is a real need pursue justice for its own sake, I have no sympathy for his plight. That's quite a different animal, than defending idiotic wrongdoing.