That's pretty common, actually. Tim Tebow's family believes that. His dad has said his missionary work in the Philippines is necessary because the predominantly Catholic population had "never heard the gospel of Jesus." They don't think of Catholics as Christians.I once had a roommate who was southern Baptist, and didn't know that Catholics were Christian. Seriously??
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Anti-Catholic rhetoric from protestants in America has been a constant since before the turn of the last century. Much of it came from newly immigrated Catholics largely being from "undesirable" areas of Europe. American protestants wanted to separate themselves culturally from them, so they denigrated their religion. The Klan once hated Catholics as much as minorities for this reason.