One reason I make sure to specify the ROMAN Catholic church when discussing it is because as an Anglican I state that I believe in one holy, catholic and apostolic church every Sunday. My denomination can properly be described as Anglo-Catholic, so there you go. Given the influence of the Roman Catholic church throughout the history of Christianity I am surprised more Christians aren't more educated about it. I've met nominal Roman Catholics who weren't as conversant with their church doctrine as I was.
Also, many Christians believe the church is not an institution as much as it is the body of Christ here on earth. The church is the people, not the building.
eta - I was reminded of the scene in "Angela's Ashes" when Frank throws up after his first communion, and there is a debate as to how to clean it up. With holy water??!!