“Sensible justice policy” no I think you are so full of yourself as to take it as a given that your opinion is correct and there is no possibility you might be wrong.
“because it is bad for society” well I mean you said that as fact so it must be true. I mean the British legal system has clearly produced a society of barbarians with its policy of upholding all law breaking as criminal and then adapting punishments to suit the moral context of the crime. On the other had the US system that acquits people if it deems a crime was excusable is famous for being the paradigm of virtue.
Now I will not claim that there is not the possibility that this is down to other differences in the legal systems and cultures. But at least I am showing some evidence and making some argument instead of just giving opinion as fact.
I agree that the rule should be allowed to be challenged, however he did not. He went straight from warning to breaking it without ever once seeking permission.
We have systems in the UK to allow laws to be challenged without breaking them, in fact if the law is overturned after you broke it you are still likely to be charged. This is to maintain the status quo. The law is not a real thing, it only has the power we give it, therefore in the UK we maintain a policy of upholding the law until it is changed.
If a person resists arrest and is then found innocent of the crime for which he was being arrested should he be done for resisting arrest? I believe yes as that makes the law have a value. If the law only applies if you are guilty then those who believe they are innocent are encouraged to ignore it.
In the same way if a law only has meaning if it is just then those whose moral view is different from society as a whole have no strict guide as to what is wrong and what is not.
In Britain most of our law stems from common law, this means that it is the will of the people that it is upheld. New laws must then slot into and establish common law. This answers your problem. The law may be wrong but the people of Britain agree with it. If you break it you are punished. If you were pushed into it you are still found guilty and still punished but a judge/magistrate may be lenient in light of mitigating circumstances.
I disagree with the claim that ‘it is the law’ is not reason enough. That enforcement is what gives the law meaning. Otherwise the law is moot and we are simply deciding post-facto if a person is conforming to society. That sounds far more dystopian to me than a world in which you may be denied a minor liberty for the duration of an appeal process to determine if a law is just or not. It also stops people being unjust in the duration prior to it being decided that the law is fair. especially as 90% of the laws are judged and established under the verdict of a jury of your peers.
Lastly the school has a role beyond maintaining order and discipline (which in children requires a greater tend towards the authoritarian than in the real world… are you made to wear a uniform? Punished for non-attendance (beyond not receiving wages not earned or losing a job you failed to do)? Forced to eat according to set regulations? Set work to do in your own time, unpaid? Forced to exercise? Tested continually? Disciplined for language, thoughts, etc? and so on). A school must teach a child to be part of the society he is growing towards. In that society he must conform to laws, even ones he does not understand. If he disagrees with them then he must protest through the proper channels. By enforcing no rule breaking the school teaches this. By forgiving him crimes it endorses the notion that he need only comply to rules he agrees with.