Most of the claims you mention are seriously flawed and have been debunked. But even if we grant them for the sake of argument, the prepuce has withstood the test of natural selection. Whatever detriments that the prepuce poses are necessarily outweighed by the benefits conferred by it. You would need to show some mechanism within natural selection which is causing the prepuce to be retained in spite of what you believe is a net determent. Natural selection has quirks such as evolutionary path dependency, which could be argued. The prepuce however, exhibits a range of variation in length, and there is therefore a very clear, and short, evolutionary path to eliminate it. Natural selection is by orders of magnitude the grandest, and most definitive “study,” and the results are clear. Thus the removal of the prepuce is necessarily detrimental to the victim—and no amount of data from pro-mutilation doctors can show otherwise. The real question that should be studied, is what are the detrimental effects of male genital mutilation.