Reason #2 – Teens’ and twentysomethings’ experience of Christianity is shallow.
I've been saying it over and over. STOP. WATERING. DOWN. THE. FAITH. Young people want to be challenged. They want something to rebel against. They know something is terribly wrong in the world and they aren't fooled by the happy-clappy catechesis they've been getting. I'm not saying we do away with crafts and break out the nun's discipline rulers, but I am saying we need to start teaching the whole of our faith and we need to do so in a way that emphasizes dynamic formation and real world application (including relationships with peers).
Reason #5 – They wrestle with the exclusive nature of Christianity.
Again, we need to start teaching the truth. I think we tend to fall into one of two major errors. The first is that we shriek in fear whenever our kids encounter another religion or philosophy. We don't engage these ideas (when applicable), but quarantine them. The second error occurs when we pretend other faiths (or even denominations) are exactly the same and there are no differences. This is exactly how we get Buddhist poetry read at Mass. Niether of these errors is in keeping with the truth and so niether of these errors can ever be truly loving. In the words of G.K. Chesterton: "Love is not blind; that is the last thing that it is. Love is bound; and the more it is bound the less it is blind." We have to accept the truth that there are real and serious differences between faiths, but that doesn't mean we can't love each other and be decent human beings.