I think our understanding of another is difficult because we are coming from 2 different approaches.
I can see what you are saying. From a viewpoint that does not believe in the type of spiritual rebirth you are talking about, I would say that if you examined a "born again" Christian in minute detail- their thoughts, beliefs, attitude, prayer life, and their intimate view of their personal relationship with Jesus and compared it with the people who are posting on this thread when they were calling themselves "born again", you would find no difference.
To you, I think you are saying, it is because either they were not truly in a relationship with Jesus or that they were and will one day return, being inevitably drawn back to that which they cannot resist.
To someone who does not believe in Jesus anymore, they have experienced a great loss, because whatever you say cannot undo the fact that their beliefs, their relationship to them was genuine, full of meaning and often the be all and end all of their life. And not believing as you do in this spiritual rebirth, they quite rightly point to you and say, Rad, I was once like you.
Until suddenly, one day, it all became so much straw.