Syag Lchochma – Its the 4 inches that I find offensive. People are being taught things that have no basis in Halacha. This leaves us with Am HaAretz Jews who have a set of rules that they follow, but no understanding of why they exist or where they come from (or even if they make sense, which this one doesn’t).
My suggestion: Teach the Halacha (skirts must cover the knee at all times) as well as why (Kriyas Shema, Rishonim, etc.) and people should be able to understand what their own body covers require in order to follow the Halacha.