Well, I have known three who were "shown to be righteous" who are no longer Christian, one even an atheist. I would be willing to bet that you think that by "justified" James means "shown to be righteous", therefore, it's possible to prove to people you have a true, saving faith. Believing this interpretation of James 2 makes it kinda hard to hold the position that EVERYONE who backslides "was never saved in the first place". Either it's possible to "show" true faith, making it possible to lose salvation, or by "justified", James doesn't mean "shown to be righteous". You can't have it both ways.
Have you ever known anyone who has shown a true faith, yet reverted back to a life of sin?
Actually it would be illogical for you to argue against the second question...So therefore the answer for the second question is no. You asked me 'Can a person who has been born be "born again"? Read the conversation between Jesus and Nicodemus in John chapter 3 and you will find your answer.
No, you have constructed a non-sequitur. This is your "gotcha" line on this topic, but it doesn't follow. I'm sure you'll agree that Jesus is talking spiritual rebirth, and I'm sure you'll also agree that physical rebirth is impossible. You are trying to make the case that because it's physically impossible to become "unborn" then it's spiritually impossible to be come "un-born again", or unsaved. It doesn't follow.
If it's spiritually possible to become "born again", a physical impossibility, then another physical impossibility, becoming "un-born" is not logically ruled out by this analogy. It is possible to become spiritually "un-born", if you want to put it that way, even though it's physically impossible, because it's possible to become spiritually "born again" even though it's physically impossible.