HammerStone said:
Aspen, I think you touched on a key point. Many folks are rejecting a Christianity based in too much "rationalism" (IE: the concept that every single thing can be systematized) or that there are often irrational (though they may seem rational to deceived believers) predictions and focuses on things over and above Jesus.
There are a couple things that I want to point out in fairness. Number one, much of the declines we are talking about in this thread - both in Europe and America - are related specifically to Caucasians in terms of secularization. For a counterpoint, I can provide both Africa and China as examples where Christianity is, well, growing like wildfire. Here in the states, if you separate out the Black and Hispanic believers, there is a much smaller rate of decline, and is even growing in some sectors.
Here's a great link on non-white millennials from Faithstreet:
http://www.faithstreet.com/onfaith/2014/05/16/are-millennials-really-leaving-church-yes-but-mostly-white-millennials/32103
Dr. Anthony Bradley has also talked about this a good bit if you follow him on social media, or check out this blog entry:
http://www.dranthonybradley.com/a-gentle-friendly-request-for-southern-baptist-writers/
I've seen all that too and I think for the most part it's spot on. It seems as a population becomes more developed, economically advanced, and educated, it become less religious. It's an interesting phenomenon.
Second, I'm not sure I fully buy the young-leaving narrative.
The data is pretty clear; they are leaving in significant numbers.
I would suspect that a lot of the nones are young because it's easier for a young person who has grown up in the rapidly secularizing environment to leave. However, I really don't buy it's just an issue of cranky and rude old folks. Yes, the church has been quite disconnected in some areas, but there seems to be a notion that if older adults were nicer, there would be more young Christians. To me, this is describing a very shallow faith, more in line with Moralistic Therapeutic Deism (MTD) than Christianity.
No, no...it's definitely not that simplistic. Here in the US, I hear a lot of older Christians lament how politicized Christianity has become, and how often church members are subjected to what they call "purity tests", where if a person say, votes for a Democrat, they are ostracized, or it's discovered that they don't support tea party groups. I've even attended services at some churches where entire sermons are dedicated to nothing but upcoming elections! That's not why a lot of people go to church, and when they see that sort of thing, they start to look elsewhere.
There's also the factor of younger generations being more educated. That means they're going to colleges and taking world religion, philosophy, world literature, comparative religion, and other similar classes where the Bible isn't treated as the direct Word of God, but as one type of religious literature among many. Also, in going to college, they encounter a lot of other students from diverse cultures and backgrounds...and believe it or not, they all get together and talk!

And in those discussions, religion comes up a lot, and the kids who grew up in Christian households will be exposed to a bunch of "This is why I'm not a Christian" arguments from their fellow students. In all, it means they're exposed to a lot more different ways of thinking and believing than previous generations.
Of course you have to throw in the fact that kids today are getting better and more thorough education in the sciences too, and the fact that many US Christian denominations take extreme anti-science stances. I can understand the whole creation-evolution thing, but I've also seen Christian groups be global warming denialists, anti-vaccine, anti-modern medicine, anti-conservation, and a handful of other anti-science advocates. And it doesn't make sense to me. There's nothing in Christianity that has anything to do with those things, but somehow they've become fairly prevalent in Christian circles. I suspect it has to do with conservative Christianity's overlap with the corporate interests of the Republican Party.
Add in the strong perception that Christianity is decidedly anti-gay people too. As we've been over here before, it's one thing to say "I believe homosexuality is a sin" or even "I believe marriage is between a man and a woman", but it's something else entirely to spend significant resources trying to deny gays basic civil rights (e.g., employment discrimination protections, housing, hospital visitation). If you pay attention to Christian groups like Focus on the Family and Family Research Council and some of the hateful things they say about gay people...well, it's almost impossible to come away thinking "Well, they just think being gay is a sin, but they don't hate anyone".
None of these factors by itself explains the exodus of youth from Christianity. But put them together and they do. Also, I spend a lot of time listening to what teens and twenty-somethings have to say about Christianity, and it's quite eye-opening.
While the nones trend is alarming for anyone who does not want to see a single soul fall into hell, I am not sure that this will be a longer term trend. I am reminded of the old Churchill quote about young liberals and old conservatives. Many of these who have left will be back. It is a lifetime journey.
That could be. I certainly hope so.