A very common objection to the Catholic Church is the hierarchy. Many Protestants claim that the Pope is not only not scriptural, but just plain wrong. To this, I pose the following riddle.
A Southern Baptist, Oneness Pentecostal, and a Jehovah's Witness are in a police deposition room. On the table in the middle of the room, there is a King James Version of the Bible. The three people have each studied that Bible thoroughly, and have come to mutually exclusive understandings of who Jesus is. The Southern Baptist holds the traditional understanding that Jesus is both God and Man (the Trinity), the Oneness Pentecostal believes that there is only one Person in God, and that he manifests himself in different ways (an ancient heresy called modalism), while the Jehovah's Witness believes that Jesus was really only an angel (a form of Arianism). They begin debating who is right, throwing scripture quotes at each other until they're blue in the face. You are watching this, and with you, there is a person who has never before been exposed to Christianity. He turns to you and asks, "How can I know who's right?"