I hesitate to disagree, as an outsider, and take your comment as accurate (sadly). Much of this I'd argue is lack of understanding/knowledge. How many RC have a deep understanding of their own dogmas/theology/history, much less another those of another church.  Then there is the destructive soul-crushing temptation to turn faith into a cult, particularly a cult of exclusivity. Shouting "one true church; we're in, you're out for eternity" is intoxicating for some. The human need to be "better" than another in some way, any way.