Cultural Inertia is a powerful thing. As a parallel, docking a dog's tail, clipping its ears, or declawing a cat is considered inhumane, but routine neonatal circumcision is accepted and defended. Why would an aesthetic modification be unethical on a pet animal, but encouraged for an infant human? If something is culturally accepted as normal, it's a lot harder to critically examine it.
I tend to find acceptance of neonatal circumcision and declawing in the same societies.
To me it's pretty simple; unless it's medically necessary you don't do anything (in the context of irreversible medical procedures) against a creature's will. Be it human or otherwise.
