I absolutely do, within reason and within legal limits, school kids should be able to wear whatever they want as it’s a big part of their self expression.

Also, for things like art class, which can and will get very messy, very fast, especially with younger kids, school uniforms are just flat-out impractical vs. wearing old clothes you don’t care about, eg. for clay day or for paper mache day or anything else like that, although ideally for stuff like this, you’d provide some old slightly oversized shirts to begin with that can be smudged with paint or clay or whatever without fear, effectively acting as smocks.