Others pointed out the Catholic Church is hardly a marginalized entity. It is different when people "dress up" as Native Americans—their culture and traditions were practically destroyed (by European Christians). The Church, on the other hand, is one of the biggest financial powers on the planet. They can handle Rihanna in a Pope hat.
Hardly anyone is really offended or put off by this year's Met Gala appropriating Catholic symbols and iconography most likely because the Catholic Church is pretty much a global superpower. Appropriating these religious imagery does not hurt them or marginalize them in any way.
The accompanying art exhibition received the official stamp of approval from the Vatican, which actually loaned the Costume Institute garments for the show. If the Vatican is cool with the idea, maybe American Catholics need to calm down.