This would seem to be restricted to people who were willing to say they were Catholic.
It would seem that way until PICO organizes some group (may be Catholic or Protestant or even both) in your town and suddenly you find civic priorities are being decided at protest meetings directed by PICO organizers. Having worked with PICO, I learned that what they are about is gaining power for PICO, and the people they “organize” are just pawns in their game.