St. Mark was the one who started the Coptic branch several decades after the Resurrection. He was an Apostle and also a Gospel Author. Are Coptic Christians the REAL Christians because of it?
Not EVERYONE! We have relatives who are Jehovah's Witnesses and have no problem with them. Mormons don't present us with any problems either. Scientologists, on the other hand, are way-out weird. I mean Tom Cruise is their shining example and who is weirder than he is? Just my 2 cents' worth JG! :)
There is unfortunately a lot of truth in your "there is a certain amount of "in fighting" among Christian denominations and name calling like, "They aren't Christians." In my eyes...A christian is a Christian" And it applies to any organisation. religious or otherwise, as soon as it has an offshoot.
btw "Muslims...(Shiite, Sunni..blah blah blah) believe in Allah" is not strictly true, Christians, Jews, Hindus, Sikhs and other theistic religions believe in Allah if the have Arabic speaking followers. Just like in English the supreme deity is called God, irrespective of religion, so does every language have it's own word for the supreme deity, irrespective of religion. In French God is Dieu, in German Gott, in Spanish Dios and in Arabic Allah.
Branches, denominations, cults...whatever one wishes to label them, are man-made.
True Christianity is a personal relationship with God, trying to emulate the love and forgiveness that Christ both taught and lived, and working/studying to be a better person.