Usually, people go off the derech when they are teenagers, sometimes later, sometimes earlier.. Sometimes they say that it is b/c they had "questions" on Judaism and their reasons for leaving were "intellectual".
Rav Shlomo Fischer ztz"l who was recently niftar is a great case study. He was an off the charts genius. Nobody who goes off the derech is nearly as smart as he was. Not even close. He also knew EVERYTHING in Torah. Not only Shas and Poskim but the Moreh Nevuchim and all the other books of Jewish philosophy [he was a great expert in the writings of the philosopher Rav Chasdai Crescas and edited a new edition of the sefer אור השם]. He also knew a LOT of general philosophy. He knew it and he knew it well. He knew about Darwin and his *theory*. He knew all about it. He was also a well thought out person. All day every day he was thinking. He was VERY independent in his views. He didn't toe the "party line" on anything [and was quite frank and candid in expressing his views]....
Yet - he was a very devout Jew, to say the least. He was careful about every Halacha and really believed in Hashem, Torah Min Hashomayim and Torah Shebial Peh.
So take the average guy or girl who goes off the derech. How much do they know? Very, very little. They have never learned מורה נבוכים - or for that matter Rav Amiel's לנבוכי התקופה or the Rav ztz"l's לנבוכי הדור. Three amazing sfarim for the "perplexed". A person is perplexed? Read and see what happens....
They don't know Maharal who dealt with many philosophical issues. They are not experts in the writings of Rav Soloveitchik who was quite the philosopher. The list goes on....
Do they have a proof - ONE SOLE PROOF - against the existence of G-d? No - such a proof doesn't exist. Do they have a plausible explanation for how such a integratively complex universe came into being? None.
So BY GOLLY - why are they no longer frum?? Did they think of some great questions nobody has ever thought of before? Of course not.
It is therefore my assertion that EVERY "otd" case is emotional and should be treated as such. Of course their questions should be addressed but that is not the core issue. What is the core issue? Everybody has a different story and that is what must be understood and treated.
In general - little to nothing we do in life is purely intellectual. There are always a confluence of various factors that impact our decisions. This has tremendous ramifications in life. ישמע חכם ויוסף לקח.
