I agree. It seems like you could just argue the exact opposite, perhaps more easily, that we are both Christians (or whichever) and that you just don't believe in the God that shapes your belief system. Once you understand that we both believe all the same things (killing is wrong, stealing is wrong, ect.) then you will understand why you should believe in the God that decreed all these things.

Non sequitur, and intellectually lazy. He changed the argument from the existence of god to the existence of a particular god. He also premises his argument on the idea that it is impossible to have a logical or forensically valid reason for believing in a particular god, and is therefore also begging the question.