Sex sells. Plus it's a remarkable skill. We've all been kicked in the junk before so we know how vulnerable that region is. Imagine the skill to make it invulnerable. There's an amazing possibility of martial practice. For the record, and many martial artists make this mistake, GM Tu doesn't not practice iron crotch as a method of self defense. It takes him a moment to bring his qi up so it has no use in real combat, and being a former sparring champ, GM Tu is fully aware of this. Iron crotch is a qigong practice. You do it to increase your vitality and that, in turn, feeds into your overall power as a fighter.