Argument: Circumcision was used to reduce fertility of certain groups
"Cutting the competition". The Economist. Jun 19th 2008 - there are several ways it may affect fertility: most obviously, the lack of a foreskin could make insertion, ejaculation or both take longer. Perhaps long enough that an illicit quickie will not always reach fruition.
Older men are in a position to form alliances with younger men—passing on knowledge, lending them political support and giving them access to weapons. By insisting that the young undergo genital mutilation of some form as a quid pro quo, an older married man can seek to ensure that even if he is cuckolded, he will still be the father of his wives’ children. Of course, the older man has probably undergone genital mutilation too, and seen his own fertility reduced. But that, if anything, increases his incentive to make certain that the young bucks are similarly handicapped. And if all the older men in a society conclude this is a good thing, it will rapidly become a socially enforced norm.