One thing he said rang true for me in light of a recent encounter a friend of mine had:
“Just look at how quickly Muslims, for example, assume Rome represents the Christian faith, and you will see how damaging her false teachings are to the promotion of true Christianity in our world today.”
This summer there was an intern in our department from the Middle East who was Muslim. I never had a chance to speak with him much, but my friend (a recent, former Roman Catholic) spent an hour one night talking religion with him.
Turns out that during his stay here in the US, he was rooming with a Roman Catholic who unfortunately ended up representing “Christianity". This Muslim young man was happy to learn from his new Catholic friend that they actually worshipped the same God and were able to come to a “I’m okay, you’re okay” consensus.
My friend did what she could to undo some of the damage, specifically in emphasizing the divinity and centrality of Jesus in the Christian message, but this man had already been warned by his Catholic friend to disregard “other Christians” who claimed Islam was incorrect. “Just tell them to see catechism #841” the Catholic had told him (he actually had the number memorized).
This is one of the many reasons that Roman Catholicism is worth opposing. Not only is Rome leading her own fold in the wrong direction, but she is a false witness to the one true gospel for those outside of her dominion. Personal experiences like this make it difficult to just stand on the sidelines and play nice as some would prefer.
"The plan of salvation also includes those who acknowledge the Creator, in the first place amongst whom are the Muslims” CCC 841