These two things are not mutually exclusive. People back in the day were just as smart as us, it’s likely they noticed people who had their dick snipped were more likely to not-die, and so it became a religious mandate. A lot of religious dogma has a basis in functional routines or hygiene. Think of how Islam asks you to wash yourself before praying. Yes it is because you’re presenting yourself to God, but also because people realized washing yourself often seemed to have a positive effect on your health, maybe you got sick less often, which sounds like a blessing, doesn’t it?