Can I be both Catholic and Mormon?
Notice that all the Quormons here say "No Way" while the Catholic says "Yes".
I hate to disagree with my fellow Saints' monocular vision on all things religious, but Mr. Flynn is correct. In the eyes of Catholics, a baptized and confirmed Catholic is still a Catholic even if he indulges in some Latterday-Saintery later in life. The differences in perspective are similar to the different ways different nations view citizenship. The United States think you can have only one citizenship, if you become a US citizen you should forsake all others. (This is the Mormon view). But other countries are just fine with having split loyalties and dual citizenship (The Catholic view).
And to be fair, Mormon aren't that much different than the Catholics when it comes to keeping you registered on their permanent head count no matter where you go later on. Once they dunk you, you are FOREVER on their records and they consider you a Mormon even if you move on a become a Rastafarian or a Sri Rajneeshi. If you never pro-actively ask to have your name removed from the rolls, they'll always count you. They currently count some 16 million members when most realistic estimates of the active faithful only range from 4 to 6 million.
Want your mind further blown? You can be a Catholic and a Muslim and a Mormon all at the same time.
How so? Islam doesn't require you to believe, simply obey. Here's how you do it, first you're baptized and confirmed a Catholic. Then at some point you meet an Imam and he convinces you to convert to Islam, and you convert by saying "There is no God but Allah and Mohammand is his prophet" three times. Congrats, you're a Muslim, now you just have to obey. So you commence obeying all the rules of being a Muslim, you pray five times a time, etc., even if you don't necessarily believe it all. Muslims consider anyone who follows the rules of the faith to be a Muslim regardless of when they lived or what they believe. Jesus was a Muslim for that reason. Obedience to the rules is the key. So don't drink, don't eat pork, make the hadj, study the Koran and think whatever you want.
Then this same Catholic/Muslim decides to become a Mormon, but this time he has to believe the JS story because his new faith wants to make sure his "mind is right". Let's say he does this but at the same time he keeps up the Muslim observances, many of which dovetail nicely with his new teetotalling Mormon faith, so its not too much of a stretch. Think of his continuance with the Muslim observances as if he were a Mason practicing the Masonic rites. You can do that and be a Mormon at the same time even though it's a bit incongruent. He could just about pull it off.
So He's Catholic no matter what, Muslim if he observes but not necessarily believes, and Mormon if he gets his head right and does all the rest.
Hell, for that matter if this same guy were born a Jew of a Jewish mother, circumcised and made it to his bar-mitzvah, then was baptized and confirmed catholic, then became a Muslim, then became a Mormon he'd have four bases covered.