Why it it legal to circumcise baby boys in the u.S.?

Personal decision. This procedure, with religious underpinnings and some health advantages, is a personal decision usually of the parents. There is no reason to legally interfere in this personal decision, and it is an obvious personal choice.
Why Shouldn't it Be? Analysis of all research studies regarding circumcision, conclude that there is a positive health benefit to performing the surgery.This does not consider the religous aspects. Given the health benefits, why should there be any question regarding legality.