I think what many people miss in trying to discuss circumcision from scripture is that modern circumcision is nothing like what God commanded in the Bible. It is a far more extreme operation, and exists for completely different (and secular) reasons.
In the Scripture, people were able to circumcise their children with a sharp stone in the middle of the desert, without the child dying. Furthermore, guys routinely had the operation done as adults, and seemed to recover within a few days, without anaesthetic. Have a think about this. There is an enormous amount of tissue removed in a modern circumcision, and bleeding is prevented using fancy little devices that are a bit more high-tech than a sharp stone.
In the Old Testament, circumcision was a very minor operation, with only the very tip of the foreskin removed - thus there was little bleeding and recovery was rapid. However it was possible to hide the "mark" of circumcision by pulling the remaining foreskin down (since it was still nearly complete), and encouraging regrowth (which takes little time in that situation).
To avoid this, at some point (maybe 140AD, but sources differ) the Pharisees introduced a more severe operation, approaching modern circumcision, which could not be hidden. Note that this was not scriptural, but the new traditions of man. This was never practiced by Christians as the Catholic church banned circumcision.
Then in the late 19th century a few people started thinking that masturbation caused a range of health problems (not true, not commenting on the moral side of this just the medical). Kellogg (cornflakes inventer) was a key thinker in this area. He promoted the idea that people should eat a spartan, cereal-based diet, males should be circumcised, and females punished for masturbation by applying carbolic acid to the clitoris
. The new form of circumcision promoted was designed deliberately to reduce sexual pleasure, and was particularly extreme, removing the entire foreskin.
This new idea was promoted for American soldiers in the World Wars, and in a few countries such as ours who are heavily influenced by American culture. This resulted in many people receiving it and it becoming the new "normal". But the origins and reasons for this modern practice are far from scriptural, and should never be argued for from scripture. They are purely medical, and the bulk of international medical opinion these days is that circumcision is not recommended due to the health problems it can cause.
Why cut off something just in case it gets sick? People used to remove tonsils in case people got tonsillitis, an idea popularised at a similar time to the modern circumcision fad, and it caused no end of problems - God made tonsils for a reason, and doctors know that now. The same goes for the appendix. Should we cut off women's breasts just in case they get breast cancer? God created a foreskin for a reason, and it fulfils an important role. He never commanded anybody to remove it either, just trim the end as a symbolic sacrifice to Him. Removing it is an invention of man (pharisees and later Western sex-phobes), not scriptural.