With regards to the First Amendment and religious freedom, there are limits. If a practice causes harm to others, it is on grounds for being outlawed, even if it is a part of their religion.
Circumcision causes harm to infants because it is the amputation of a body part without any significant pain reduction, creating the risk of the baby dying from bleeding, infection, or shock. Circumcision creates no benefits that override such risks.
Studies that try to show that circumcision is beneficial are biased and badly done. They try to show that circumcision decreases the risk of STDs. Such studies were done in Africa, which is HIV/AIDS rampant. They ignored European and Asian countries, where men are not circumcised and have lower STD rates. Also, even if it did reduce the risk of HIV/AIDS, the amount that it did would be so small, it would be completely overridden by the cons of circumcision, which include the loss of many pleasure-causing nerves, the increasing of friction during sex, the karatinizing of the glans, etc. Circumcision is not a substitute for safe sex practices or abstaining from sexual activity all together.
The removal of genital structures of baby girls is outlawed, and the folds of the vagina are much more prone to smegma than the male foreskin. As such, there is an underlying factor that still allows male neonatal circumcision to continue.
Circumcision got started in the U.S. by someone called John Harvey Kellogg. He believed that masturbation was worse than war, bubonic plague, and smallpox, which is absolutely rediculous by any standards. He suggested that circumcision without any painkillers was to be used as a punishment to boys who were masturbating, and girls would have carbolic acid poured on their clitorises to make them associate sex with pain from then on. Allowing neonatal circumcision of boys to exist would keep this sick man’s legacy alive. The U.S. has already taken its first big step by outlawing neonatal female circumcision; it’s time to finish the job and outlaw it for males as well.