Not a direct analogy but it's now illegal in the UK to dock dogs' tails unless they are a working dog which specifically needs it (for some spurious reason). Amazingly, a lot of show dogs in breeds where docking has historically been done are working dogs who have to have their tails docked. Who'da guessed
I imagine that circumcision will be allowed where there is a medical necessity for the procedure to be carried out. A large proportion of people in religious and/or ethnic groups where circumcision is the norm will find doctors who will certify that the circumcision of their boy is a medical necessity.