Your idea of a issur d’oraysa, is not all that clear cut actually. And television and the internet have plenty of material on them that is a violation of tznius. Are you saying that it’s worse to wear a skirt above the knee, than to expose your family to all sorts of tumaa?
But as long as you’re picking and choosing, which warnings from the Gedolim to take seriously. And proposing courses that they didn’t approve…