"Uniforms at schools are designed to put every pupil on a level footing, so they are essential to prevent the "I have better designer wear than you" syndrome, or in this case "I'm better than you, because of my cultural hairstyle".
I'm not convinced, and this really depends where you look. In an urban-based school where kids are far more likely to see each other outside of school anyway, they won't do anything to stop such attitudes. In a rural setting (such as my old school) where pupils are less likely to see each other outside of school hours, I admit this might have more credence. But it still looks a pretty thin excuse to me.
"Or are you against all types of uniforms? "
Of course not. The difference with the police (not all of whom wear uniforms) and military etc. is that these are all positions that you make a conscious choice to go into - and are thus have far more reason to take pride in a uniform. Kids do not choose to go to school - while they'll be aware they weren't always in school, your average schoolchild will be unable to remember not being in it. They're simply herded into these institutions for as long they're sentient and then badgered and barked at for not conforming to rules which are fairly arbitrary and which they have no real reason to have any faith in.
baz: When I said 'within reason', I was precluding something like a t-shirt with expletives all over it or something. And I admit the argument I was making was much wider than this particular case.