....Sounds like the little horn in Daniel, the one with the...mouth speaking pompous words against the most high. (to me, anyway).
You all are probably...in your lives....wonderful Christians. This is not to gainsay that possibilty. It's just that...how to say this?....look, try...please try to imagine what it's like to hear that one could not be saved....unless one were a Catholic. Can you at least understand a little?....and no....it's not some devil motivation or darkness that causes rejection of that collection of "great words" (against the most high).
The hope, -- hope being the first theological virtue -- is that one becomes Catholic on his deathbed, because Christ will convert him. The Church, incidentally, gave it a great deal of thought as it had to confront the pagan culture. It is not a new teaching.