Question to those who circumsize their sons for religious reasons?

I am not religious at all so please help me to understand how if there is a God and he created man with a foreskin why on Earth would he expect you to cut it off and cause excruciating pain to a new born child. Especially when it has such an important function. That just seems so wrong. To me it is like cutting off your eyelids they have a purpose as does the foreskin, I just find it to be so cruel and barbaric to welcome a new born into the world in such a horrific way, I feel that removing a child's body part without his consent is unacceptable. I have a 3 year old son and if God himself appeared before me and told me to cut of a part of my son's body I would tell him to go to hell! I will not mutilate my child's genitals for anyone!!! If God wanted man to not have a foreskin he should have made him that way and spared him any suffering. That would be the kind and humane thing to do!!! I just don't get it!!