In my experience, people don’t make drastic changes in their lives unless they’re either super special, or a little messed up. You’re entitled to think that “those who choose to leave Orthodox Judaism, or dont actively practice it” are super special, but IMHO they’re a bit messed up.
I read an autobiography of a woman who suffered from schizophrenia. But she had good middos. And she came to the conclusion that if everyone thinks that the voices in her head are illusionary, they’re probably right. She is currently a psychiatrist who treats Schizophrenics by telling them her story.
This guy seemingly has a problem with Emuna. He can either believe that all of Klal Yisroel since Moshe Rabbeinu are ignorant fools and he’s wiser than all of us, or he can realize that so many super brilliant people are probably, or at least possibly, right. It all depends on his middos such as Emes and Anovoh.
??? ????, if he wants to go OTD and he’s looking for an excuse, he’ll probably do that in spite of your arguments and reasoning. If however, he wants to do what’s right, but he’s confused, and he has the humility to realize that he’s not smarter than all of klal yisroel, he’ll inevitably come to the conclusion that he’s the one who has the problem and he’ll search for the solution.
Hatzlacha Rabba.