The "crux of the issue" both sides of the fence , by what they have been taught, perceive that the other side is wrong & in need of instruction to the contrary ...
Many have opinions of other denominations , because of what they have "heard" from some one , some place .. being on the " outside , looking in " and perceiving that "different" is wrong ...
Catholic book stores have a small text " Scriptural References to the Baltimore Cathechism " which will give you chapter and verse to respond to detractors .
Many have been taught that none of the 7 books in the Catholic bible are mentioned in the New Covenant , not understanding the foot notes in the NAB OR DR text , nor that the question of the Pharisees about the woman who had 7 husbands was from the book of Tobit
Many wonder about the Magesterium , Pope , and form of church government , forgetting that god told moses that aaron and his seed would be the high priests ( similar to Peter and the church ) , or that moses set up the rulers of the congregation at his father in law's suggestions ... rulers of 10-50-100-1000 ( similar to priest , monsignor , bishop, cardinal, etc)
many argue about 2, 4, or 7 sacraments (ordinances) , when all practice the 7 catholics mention ... marriage , laying on of hands , confession of sin , baptisms of water and spirit , etc.
some of the problem is one of "symantics" for we use a similar word which has a different meaning on each side of the fence ... some is the way we look at the Holy Writ ...
different , is not wrong , just different