Male circumcision is the process of cutting or tearing off the foreskin of the penis. This not only removes most of the 'fine touch' nerve endings from the victim's genitals, but also robs him of the proper functioning of his penis. In an intact male, the foreskin serves several functions...
* It keeps the glans moist.
The glans (and the inner foreskin) is mucossal skin, thus it must remain moist. If it dries out, it becomes much less sensitive. Another good example of mucossal skin in that of your tong, if you have ever had 'dry mouth' you know that it looses a lot of sensation when dry.
The glans is not supposed to be exposed all the time. When it is robed of its protective organ (the foreskin) it dries out, and develops a layer of dead, dry skin to protect itself from friction/air. This act is called Katernazation. Once this happens, the glans becomes much less sensitive, loosing the ability to feel fine texture. It is similar to wearing rubber gloves and trying to feel the texture of a orange.
*It acts as a lubricant
The USA is the only nation that alters most of its boys for non-religious reasons (17 out of 20 of the world males are intact). It is no wonder then, that the USA is one of only a handful of nations in which sexual lubricant is common. The perception in the USA is that the female genitals are solely responsible for the easing of friction during sex. This is not true. The male foreskin provides a sliding motion that greatly reduces friction. See it here.
*It provides sensation
The foreskin provides sexual stimulation to both the male and his partner. It contains the vast majority of 'fine touch' nerve endings, the ones responsible for texture sensation. The average male foreskin contains tens of thousands of nerve endings. Also, as stated above, the foreskin protects the sensitivity of the glans. For the woman, the foreskin retracts and bunches up on the shaft. This added texture directly stimulates the highly sensitive outer section of the vagina. Think 'ribbed for her pleasure'.