Well I agree this issue is fairly black and white "People should have the right to control their own bodies short of a medical emergency."
How could someone disagree with that?
That is because people INVEST other issues in the circumcision issue, and by attacking circumcision, to them it feels like your attacking that other issue as well.
For example a jewish parent may defend every action they make about circumcision and seem "pro-circ" because to them it feels like your attacking their culture. In their mind saying circ is bad, (to them) feels like they are saying there is something wrong with their culture.
This is same for mothers who have invested circumcision as a sound parenting decision, admitting it is bad, (to them) feels like admitting they are bad parents.
For men in American society they have been conditioned to see a circed penis to be "better" (instead of just different) and maybe even more manly. To admit circ is bad is like questioning the very culture which almost defines them.
Body modification has always been an important, and powerful practice for cultures in the past (and will continue into the future). Perminatly altering a part of your own body is a VERY powerful experience in life thats why people easily take what is important to them in their lives, and connect it to circumcision. So for "them" questioning circumcision is like questioning the most important things in their life.
I dont think we will ever get rid of body modification (and honestly, I dont think we should) but we need to do everything we can to adjust societies perception on this, and remind our country and our world that as important as these types of practices are, we cannot be performing them on children.