Tznius definitely causes much stimulated discussion.
Bottom line, tznius is not only halacha, nothing is. A jew can be a person who strictly adheres to exact halacha guidelines and be considered a menuval bereshis hatorah and go straight to hell. In fact, the consencus is that the bais hamikdash was destroyed because of a lack of lifnim mesharis hadin. So even if 4 inches isnt halacha, which many prominent Poskim publicly state, doesnt matter. Anyway, can anyone list a Rav that doesnt suggest this? Didnt think so. Yes, its very hard to keep (why, is another discussion for itself. Is it the Yetzer Hara? Is it because so many people suffer from low-self -esteem that cause women to want to stick out and cause people to gaze at them? Possible. I think if we all realized our self-worth and that every positive action of ours has an unbelievable affect on so many levels, including heavenly spheres, and in turn, earth, we would be willing to raise out standards in all areas. May we all grow together.