It would just teach students to suppress their individuality. It would teach them that everybody should be the same, and that it is a "right" way to dress. It would also teach them extreme controversiality, and that is something i think we should avoid. This is because I think that it is a reason why society has evolved, and i think controversiality is like dwelling in the past.
Teachers should of course not wear very short skirts or a blouse with a low cut. But honestly they are adults and should have the choice to wear what they want to wear. I am, however, also against the fact that studens have to wear uniforms, so i guess i am a bit liberal when it comes to a dress code at school.