A woman may have that "defense system" that allows her to go through childbirth and a man may NOT have that same system, but I can only imagine that getting kicked in the balls is somewhat comparable to giving birth in some ways. A few of my female friends have been kicked in the kooter and have said that it was painful but only because they were kicked right in the pubic bone which is also very sensitive because of the reproductive and erogenous organs that are in that area which are also impacted by the blunt force. Believe it or not, male and female anatomy are not completely different for reproductive organs either! I know many people will argue that, but if you look at a diagram of the reproductive organs for male and female, they are literally almost inverse from one another, meaning that males have exterior and of course females having interior, but they are essentially the same tissues. As a matter of fact, the only thing that happens between a male and female during womb development is that the testicle like organs ascend into the body on a female and produce eggs, whereas a males testicles descend and become exterior and can produce semen. (later in life of course)
That being said, males and females probably have the same mechanisms, but the defense side of things is essentially muted in males since we (meaning males because I am one) dont have to give birth.
The human body, or any body, in general, is quite exquisite in its design and development.
