Masons simply require members believe in a supreme being.
They couldn't care less what religion one has.
I would be interested in knowing the Catholic opposition to Free Masons as well.
As an Eastern traveler I can attest you are absolutely correct. But most mainstream churches have banned membership in Mason Lodges.
Freemasonry tends to piss off the people that I despise. Some great men have been Masons as well.
Reads in part:
The aim of Freemasonry: the destruction of holy Church
At this period, however, the partisans of evil seems to be combining together, and to be struggling with united vehemence, led on or assisted by that strongly organized and widespread association called the Freemasons. No longer making any secret of their purposes, they are now boldly rising up against God Himself. They are planning the destruction of holy Church publicly and openly, and this with the set purpose of utterly despoiling the nations of Christendom, if it were possible, of the blessings obtained for us through Jesus Christ our Saviour.
The main purpose of the Masons is to destroy the Catholic Church.