I really do hope you never ever have kids. The attitude you have portrayed in that post is disgraceful and the exact reason why so many kids now have serious authority and behavioural issues.
There is a very large difference between respecting authority and accepting a punishment blindly when there are mitigating circumstances.
1) Parents not aware of the specific rules.
2) Said haircut being ok at another nearby school where one parent works.
3) Disproportionate punishment to the crime.
Isolation for a haircut does one thing and one thing only, damage the childs eduction. I would be teaching my kid that their education and future are far more important than the styling of their hair, and if any person would attempt to harm my childs education over such a petty thing, I would not take it sat down, which says more about your parenting than it would mine.