a humiliating kick in the crotch
It's a great misconception that iron crotch is trained in order to withstand a crotch kick. It's the same misconception that many people make about forms - that every move necessarily translates into a literal combat application. Built into the system of Chinese martial arts is qigong. People do iron crotch as a qigong discipline - the notion is that it increases vitality. In the long run, a more vital practitioner becomes a better fighter simply because he or she has more vitality for practice. That's really the essence of martial arts. You can train to fight, sure, but traditionally, martial arts cultivates one's vitality - increases the qi, if you will. got qi? If not, you can get it by lifting weights with your genitals.