I do believe that all teachers should dress professionally, but the issue becomes what the standard is of that. Obviously, looking like you are going out to a nightclub is not acceptable, but is any small bit of cleavage OK, and if so, why not? Plenty of schools already take the position that the bare shoulders of 10 year old girls are inappropriate and "distracting to boys" - and that's a sexist and patriarchal stance. Female bodies are not inherently problematic or responsible for the behavior of boys and men. That's the way they think in countries where women are forced to cover head to toe. Hence my comment.

Modesty culture is toxic and extremely harmful and degrading to women. So, yes to professionalism and no to that. What's the balance? Well, that's a tricky question that doesn't have an easy answer but objectifying women and over sexualizing them is in most cases a larger problem than teachers who don't know how to dress for work.