Kid was right. Teacher was wrong.
BUT teacher was in a tough situation, and her choice to punish all was not evil intent.
Kid should be taught that when faced with a 'moral wrong feeling' needs to ask self
1) What is the wrongdoer's motivation
2) Do I need to provide examples/trivia/data as a first wave of response
I've learned that providing backup data to prove my opinion is a 'second stage' in any arguement or discussion. When you jump past the first stage ("excuse me teacher, but I feel wronged" or "please explain why you are doing this" would be the first stage) people get defensive faster, because they don't see the 'hard facts' stage coming, and they feel it as an attack that bypassed the 'warning' stage.
1) "can you clarify please?"
if it still feels wrong, escalate:
2) "I feel that is wrong, and have reasons for that feeling. Why do you feel right?"
if it still feels wrong, escalate:
3) Provide trivia and backup data
if it still feels wrong, back up and find an authority to sort it out.