I've only ever had to wear a uniform for extra-curricular activities, so I wouldn't really know how Id feel about having to wear a uniform in school ALL day.
Yeah, you can't 'express your individuality' clothing-wise, but what's stopping you from doing it personality-wise?
I used to be super-opposed to uniforms, but as I grew up (see: after only 4 years out of High School), I came to the realization that my own arguments all revolved around not being able to express myself, which I felt a little silly for, because Uniforms only stop you from wearing w/e you want to on-campus.
(Well... okay... I confess, it was pictures of the Japanese school-girl uniforms that made me change my mind... >.<)
:p
In all seriousness, though, I've come to realize that while Uniforms are a big mental thing, it really shouldn't affect who you are, and that's what most of the arguments I know about focus on - the loss of expressing yourself through clothing, which seems very silly indeed.
Don't get me wrong, though; of anyone ever tried to make me wear a Uniform in my daily life - not for a job, school, or otherwise - I'd be the first to petition/take some sort of action. I rather like my 'I traded this shirt for my girlfriend (Best trade I ever made)' shirt
