Because everyone has their on personality and different ways of expressing themselves. Everyone has their own unique style. Such as goths, punks, emos, and all the girls or sporty trends. Nobody wants to feel like they are the same as everyone else.If the schools want students to dress how they want then they should lay out a dress code. There should be no reason to be forced to wear a Uniform.
I think because wearing uniforms curtails freedom and individuality. Each of us is unique and a uniform takes the uniqueness out of our identities as we can't wear clothes that shows and reflects who we really are.
People hate uniforms because tey want to where their own clothes.