I usually just say that there was an infiltration and what they think is the Catholic Church (V2 sect) is not actually The Catholic Church and that new structure (V2) is infested with Masons, Jews, and their enablers who are into diddling children. It's raw and blunt but it cuts to the heart of the matter.
They'll either think you're crazy (most of them) or they'll want to know more (a handful of them.)