The argument that it is "genital mutilation" is a shallow one. Male circumcision doesn't effect the ability of the person so circumcised to have sex, to feel sexual pleasure
Yes it very much does, and in fact that's the point. Here are quotes from doctors stating as such and advocating for it in the years before circumcision was a widespread practice in America:
“I refer to masturbation as one of the effects of a long prepuce; not that this vice is entirely absent in those who have undergone circumcision, though I never saw an instance in a Jewish child of very tender years, except as the result of association with children whose covered glans have naturally impelled them to the habit.” [M. J. Moses, The Value of Circumcision as a Hygienic and Theraputic Measure, NY Medical Journal, vol.14 (1871): pp.368-374.]
“A remedy for masturbation which is almost always successful in small boys is circumcision. The operation should be performed without administering anesthetic, as the brief pain attending the operation will have a salutory effect upon the mind, especially, if it is connected with the idea of punishment, as it may well be in some cases.” [John Harvey Kellog, creator of the Corn Flake, Treatment for Self-Abuse and Its Effects, Plain Facts for Old and Young, Burlington, Iowa: P. Segner & Co. 1888, p. 295.]
“Measures more radical than circumcision would, if public opinion permitted their adoption, be a true kindness to patients of both sexes.” [Jonathan Hutchinson, On Circumcision as Preventative of Masturbation, Archives of Surgery, vol. 2 (1891): pp. 267-268.] Note that he is actually suggesting that castration would be good!
“Clarence B. was addicted to the secret vise practiced among boys. I performed an orificial operation, consisting of circumcision… He needed the rightful punishment of cutting pains after his illicit pleasures.” [N. Bergman, Report of a Few Cases of Circumcision, Journal of Orificial Surgery, vol. 7 (1898): pp.249-251.]
“Finally, circumcision probably tends to increase the power of sexual control. The only physiological advantage which the prepuce can be supposed to confer is that of maintaining the penis in a condition susceptible to more acute sensation than would otherwise exist. It [the foreskin] may increase the pleasure of intercourse and the impulse to it: but these are advantages which in the present state of society can well be spared. If in their loss increase in sexual control should result, one should be thankful.” [Editor, Medical News. Our London Letter. Medical World,(1900).vol.77

p.707-8] (Note that by “sexual control,” he means having less sex, not control by the man of his sexual response during sex.)
“It has been urged as an argument against the universal adoption of circumcision that the removal of the protective covering of the glans tends to dull the sensitivity of that exquisitely sensitive structure and thereby diminishes sexual appetite and the pleasurable effects of coitus. Granted that this be true, my answer is that, whatever may have been the case in days gone by, sensuality in our time needs neither whip nor spur, but would be all the better for a little more judicious use of curb and bearing-rein.” [E. Harding Freeland, Circumcision as a Preventative of Syphilis and Other Disorders, The Lancet, vol. 2 (29 Dec. 1900): pp.1869-1871.]
“Another advantage of circumcision… is the lessened liability to masturbation. A long foreskin is irritating per se, as it necessitates more manipulation of the parts in bathing… This leads the child to handle the parts, and as a rule, pleasurable sensations are elicited from the extreamly sensitive mucous membrane, with resultant manipulation and masturbation. The exposure of the glans penis following circumcision … lessens the sensitiveness of the organ… It therefore lies with the physician, the family adviser in affairs of hygiene and medical, to urge its acceptance.” [Ernest G. Mark, Circumcision, American Practitioner and News, vol. 31 (1901): p. 231.]
“Circumcision not only reduces the irritability of the child’s penis, but also the so-called passion of which so many married men are so extreamly proud, to the detriment of their wives and their married life. Many youthful rapes could be prevented, many separations, and divorces also, and many an unhappy marriage improved if this unnatural passion was cut down by a timely circumcision.” [L.W. Wuesthoff, MD. Benefits of Circumcision. Medical World, (1915) Vol.33. p.434.]
And there's been modern research done that proves that circumcision substantially reduces sexual pleasure:
“The glans of the circumcised penis is less sensitive to fine touch than the glans of the uncircumcised penis. The transitional region from the external to the internal prepuce [ridged band, removed in all circumcisions] is the most sensitive region of the uncircumcised penis and more sensitive than the most sensitive region of the circumcised penis. Circumcision ablates the most sensitive parts of the penis.“ [
http://www.ncbi.nlm.nih.gov/pubmed/17378847]
http://www.moralogous.com/2012/04/29/the-purpose-of-circumcision-is-to-ruin-male-sexuality/