A pretty good article about why young people are walking away from the church, which you can find here.
Another excellent article written about young people who have already left appeared in Christianity Today, which you can find here.
But the most striking and widespread reason the article gives for why people are leaving is shown in this quote:
Another unsettling pattern emerged during my interviews. Almost to a person, the leavers with whom I spoke recalled that, before leaving the faith, they were regularly shut down when they expressed doubts. Some were ridiculed in front of peers for asking “insolent questions.” Others reported receiving trite answers to vexing questions and being scolded for not accepting them. One was slapped across the face, literally.
At the 2008 American Sociological Association meeting, scholars from the University of Connecticut and Oregon State University reported that “the most frequently mentioned role of Christians in de-conversion was in amplifying existing doubt.” De-converts reported “sharing their burgeoning doubts with a Christian friend or family member only to receive trite, unhelpful answers.”
Note that this says that “almost to a person” those who had questions were shut down, ignored, or given trite answers. Christians have been taught to not deal in complex matters, to ignore intellectual problems for so long, that we have forgotten how to deal with legitimate questions. We are driving people out of the church by not answering their questions.
We do our young people no favor by not discussing hard questions with them before they leave home for college. For example, in one of our Ratio Christi chapters, the student president, upon arriving at college as a brand new freshmen, discovered that he had two roommates: one was Buddhist and the other Muslim. This is more typical that we realize. Such a person is immediately forced to deal with pantheism, which embraces absurd contradictions, and another monotheistic religion who claims to have more accurate scriptures than the Christians.
If we do not prepare the students before they leave, they will get bombarded with questions after they leave. We owe it to the next generation to prepare them for the world they live in. One way is through www.ratiochristi.org.