I can partly agree, but a lot of schools will say that uniforms are used to identify which students attend which school (this is especially important for school excursions and carnivals) and also to form a sense of community and perhaps even a ‘neatness’ if the school is a particularly prestigious one. At my high school we all had uniforms, but juniors and seniors wore a different color and this was to let younger grades know who they could ask for assistance or help, much like how our captains, vice-captions and prefects wore badges to identify themselves for everyone else.
As for authors, it doesn’t bother me if they choose to have their characters wear whatever they want at school or if they choose to apply school dress codes and uniforms since every school is different and so is every story. I can agree though, that it isn’t nice to shame someone for what they wear, however something very indecent must be brought to attention to deter it from happening again because it can be totally inappropriate or even offensive (in any setting, but specially an educational/school setting).