A comment to an earlier post raised the question of circumcision more broadly:
Whatever the free excercise clause might mean, I don't think it meant that people could do irreparable physical harm to their children. Likewise, if you have legal guardianship of a child, do you have a legal right to perform other kinds of unnecessary cosmetic surgery? Why stop at circumcision? What is the limit on what harm a parent can do to a child?
We would not accept the mutilation of young girls, no matter how strong the religious convictions of the parent. Why would we accept the mutilation of young boys?
I agree that female circumcision (or, if you prefer, female genital mutilation) should be banned, but that's because it's pretty clearly and severely harmful to the child -- unless I'm mistaken, there's a near certainty of substantial loss of sexual pleasure plus (I think) a substantial risk of other problems.
The matter as to male circumcision, I think, is different. While some people claim that it causes a loss of sexual pleasure, there's a hot debate about this, and there's little reason to think that the loss approaches the loss caused by female circumcision (though it's of course not easy to compare such hard-to-measure matters). There is apparently some evidence that it has health benefits, perhaps modest and perhaps quite substantial. And there's apparently little reason to think that it has significant purely medical risks. Given this uncertainty about (purely secular) costs and benefits, it seems to me that parents should remain free to make this decision themselves. At the very least, the balance is not nearly as stark as it is for female circumcision.
This leaves the argument that the procedure, even if harmless, is an improper imposition on the child, because it's an irreparable (or at least very hard to repair) change to his body, done without his consent. Yet that strikes me as too abstract an objection to be helpful.
Parents do lots of things, physical and otherwise, that can't be easily undone and that the child doesn't consent to (or can't meaningfully consent to). They may perform cosmetic surgery to correct small abnormalities, surgery that they may think is valuable but that the child might one day resent. They may give the child growth hormone to counteract what would seem to be his abnormal shortness. They may decide to get the child's tonsils removed, to avoid recurring but non-life-threatening infections. They may decide to get the child braces, over the child's strong objections.
If these steps seem likely to create significant harms, I can see the need to protect the child from them. But I'm not persuaded that a child has a freestanding right to be free of unconsented-to physical changes by his parents, independently of the harm the changes can cause.