Anyone who says that Catholics circumcise for religious reasons is ignorant of history and theology. It would take about 30 seconds and an index to find that this topic was debated by the early church, which decided that it would not require circumcision but in fact heavily discourage it. For the next 1500 years, to be a Catholic meant being uncircumcised. Circumcised people (Jews and Muslims) converted from time to time, but the expectation was that their sons would be left uncircumcised. Much of the Catholic, uncircumcised population of Sicily, Malta, Spain, and Portugal today is descended from circumcised Jews and Muslims.
When Spain conquered the Philippines, the people there had recently converted to Islam and adopted circumcision. The Spanish encouraged/forced the Filipinos to convert to Catholicism, which they did everywhere but the island of Mindanao, but for the first time in church history a group of new Catholics continued the practice of circumcision (as they still do today). More recently, the church has taken in millions of converts in Africa who had tribal traditions of circumcision which they continue as Catholics.
The Catholics in the USA (and to a lesser extent Canada and Australia) who circumcise their sons are doing it for the same reasons/non-reasons as the rest of the population. They have no tradition of circumcision and they bring up "religion" only out of ignorance and that it sounds better than "we don't know why we had you circumcised".