Sadism? Bloodlust? Perhaps it's purpose was to bind you to the group. Some people would rather believe the group, than to accept their dick was mutilated for nothing. I guess for similar reasons that the Aztecs tortured and sacrificed children. I once was told it was for hygiene, because they lived in the desert and had no running water. But if you can clean your ass after taking a shit, you can you also figure out how to clean your dick. "Truly fucked in the head" is more likely than hygiene.