The whole varna-asrama system discourages sex life. Circumcision is a facility for sex life. So in other systems of religion or throughout the whole universe the tendency is to enjoy sex life, whereas the varna-asrama system discourages sex life. Sex life is the cause of bondage of the conditioned soul to remain in the material world. If one can conquer over the sex impulses voluntarily, he conquers over the influence of material nature. So the ideals being different, I think in the Vedic system such circumcision is prohibited.
Letter to Arvind Shah, 30 September, 1975