There seem to be a few reasons why Torah observance folks leave the fold. Some go because they can't handle the demands of a religious lifestyle. Others ask questions of paramount importance such as the true age of universe or proof of God's existence and receive unsatisfactory answers. For many, Judaism is a religion of "thou shalt not's" with little positive to reecommend it. For the rest, it is the influence of secular culture and its false prophets who insist there is no God, chalilah, through weak but seductive logic. In all cases, it is a tragedy when someone abandons the faith of our fathers.
This article from Yediot Acharonot notes that one of the major factors is the rebelling against the "thou shalt not" culture that has taken over much of obsevant Judaism today:
Religious society contemplates the question of "why" - why do they become secular? The automatic answer is education. The education isn’t good enough, not strict enough. Most people believe that strictness will save their children from looking for answers elsewhere.
I think there's another way of looking at this. It is a well-established fact that from an early age, we need positive reinforcement, warmth and love. We need to be told we're doing great. At a young age this goes without saying. The parents, and at kindergarten and school everyone makes an effort to encourage us and give us a feeling of success and self-worth.
For those of us born to an observant family, another wonderful aspect is added. As young children Judaism induces warmth, and observing many mitzvoth gives a great feeling.
The religious child feels at home with Judaism. Religion is imbued with songs, dances and family rituals. Observing the mitzvoth provides another aspect of life through which our kids win compliment and prizes. It's rare to find a four-year-old who doesn't like being religious. And still we cannot argue with statistics that say 20% of these kids grow up to become former-religious.
When one looks at this process it's easy to see that the change in the approach to religion goes hand in hand with the youth's rebellion. When the children grow up, the educational tendency is to add more and more prohibitions and restrictions. The amount of positive feedback drops, while bans and limitations abound.
For some, this style works and they grow stronger and thrive in their worship of God.
But what about those who don't fit in? Those for whom spirit is as important as content, if not more so? Yes, there are religious pacifists who want to be religious without having to join God's army and serve 24 hours a day, seven days a week. They love God dearly, but interpret this love differently. They wander the system in search of someone to tell them that that's okay: different, but beautiful.
In most cases they will find out that the system isn't tolerant. There's only one truth, and their truth isn't it. Attempting to fall in line with the system creates distance between actions and what's in their heart. And the hearts don't always follow the actions. In some cases the distance becomes social alienation and ends up in complete abandonment.
This is an important point. While I don't personally agree with the politico-religious philosophy of the article's author, I can agree that there is more than one "truth" within the Torah community. One of the most terrible things a school rebbe can do is respond to an important quiestion by saying "shut up and learn some more Gemara". How productive is it to respond to a person's yearning for some form on individualism by imposing more strictures to render them a yet another bland clone?
There is also a mischevious aspect to leaving the fold. While a child who does so often does it to leave the "thou shalt not" aspect behind, the "thou shalt" remains a part-time piece of their life. They may not avoid melacha on Yom Tov but they will come home and enjoy a meal in the sukkah. They may eat chometz on Pesach but they'll attend the seder, even if only briefly and enjoy the food and win.
However, I see this as an opportunity, not a hypocrisy. While the lapsed Jew may only wish to interact with those portions of Judaism that bring personal benefit while avoiding any form of commitment, it is precisely these mitzvos that maintain some form of a connection that can be built upon. As the article notes, four year old kids love Judaism because it's all about the "thou shalt" things. As they age, they are expected to add "thou shalt not" because it's part of the process of maturing. Taking the opportunity to intelligently answer a lapsed Jew's questions in a non-threatening way could go a lot further towards returning them to the proper path than threats of excommunication and "don't you know you're humiliating the family!"
Finally, and I think this is the most important point, the Jewish educational system does a lousy job explaining Judaism to our children. A great yeshiva is defined by how many blatts of Gemara the children memorize per year or how many masmidim you can find in their beis medrash at 3 am. Yet take one of these scholars, present him with proof that the universe is 15 billion years ago and ask him to reconcile this with the literal reading of the first chapter of Bereshis and you won't get a good answer. You'll either get dismissmal or create a new kofer. What kind of system is this? It's not like the answers aren't out there. It's not like excellent literature reconciling science and Torah doesn't exist. It's not like the false prophets of atheism haven't been refuted. But no one in a position of guidance over our children learns these books. Instead, the answer is "learn more gemara" and "take on more chumros". The fact that these answers don't work hasn't dissuaded people from repeatedly using them. Which is a pity.
Children in our schools shouldn't just be taught the content of the Torah but also why it is true. They should know the anwers to the difficult questions before others ask them and provide them with lies to justify their atheistic lifestyle. This would require a sea change in educational thinking within the Jewish community but if keeping people from entering an olam shel sheker is the reward, it is well worth the effort.