Faranak Margolese wrote that one of the the reasons people go off the derech is because they are turned off by people who are closed minded and take extreme positions such as that negia is a terrible aveira. The problem is, apparently according to most opinions negia is yehareg v’al ya’avor. So her book is probably not the answer.
Usually a weak poor or broken home, and/or poor academic or social skills combine with a lack of proper understanding why we believe in judaism to lead a person to give in to their temptations.
Of course for some, a little curiousity can lead them to a yetzer hora that just overwhelms them.