This is a distraction. There is no doubt that Chaldean Catholics of Iraq, that bear the brunt of the lawlessness there, have practiced the same Christian faith for 2,000 years despite enormous odds.; I cannot think of a better example of Christians.
In case you need a technical answer, a Christian is one validly baptized who did not apostasize.
So baptism makes you a chrisitian?..
Apostatize(leave the message) from what?..