I'm sorry, but I think these stories about young people leaving the Protestants sects of the Church are all overblown. First of all, most of them rejoin when they marry and have children. Second, and I know my anecdotal evidence is just that, but I got visit my old Catholic parish last weekend. The Mass is in Latin -- all according to the 1962 Missal. The Church was filled with young people. Young couples in their 20's and 30's with 5 and even 10 kids! One couple I have known since they were high school sweethearts (they're now 27) has 5 kids. Another couple I have known for about 8 years, and I know the wife is only in her mid to late 30's, has 9 kids and is awaiting their 10th!
There are plenty of signs of hope out there. You just have to look for them.
Here is another reason:
Christopher West's Theology of the Body Webiste
Books, tapes, CDs, DVDs, etc.
Translation: They drop out of church as soon as they start having sex, and they return only after they marry and their sex lives finally become legitimized. The only ones you see in the "church singles" groups are the virgins, nerds, and outcasts (as a single I fit all 3 descriptors). These folks suffer loneliness for the Lord's sake -- or possibly they simply make a virtue of necessity -- while the rest of their generation is out partying in the world.
Tragically, the married returnees don't always come back from the world unscarred. Some (almost all women) end up in unequally yoked marriages and are coming to church alone or with their kids while the unsaved husband (or EX-husband) is off doing other things on Sunday. Others can't have kids at all when they finally want them, due to damage from abortion or STDs during their promiscuous single days, or due to wasting their fertile 20's on losers and not marrying til 30-something. And of course many others never return at all.
Not all young people get married. More and more of them don't.