Yeah, i am with Saddam on this one... If you believe that Jesus is the son of god, and that you should follow his teachings, then you are probably going to fall under the umbrella word "Christian". That being said, there are very clear and large differences in the various sects of Christianity, which I don't think anyone denies.
But its just plain stupid to argue that Catholics are not christian, when both share the exact same core tenants. Single god, same books, same son, same sacrifice, same sins. They just practice different methodologies. Not to mention that from a purely historical standpoint Protestants are simply people who wanted to reform the catholic church. The protestant sects are literally reformed catholic religions, not entirely new ones.