Every so often, there are articles about the rate at which people are leaving Christianity in America or the rate at which people are leaving particular denominations of Christianity.
While I pay attention to the demographic data, most of my understanding of this comes from having read scores if not hundreds of deconversion stories. I am fascinated with deconversion stories because I was not indoctrinated into any religion (thanks, mom & dad!) and thus I have no idea if I would have been able to overcome the kind of emotional manipulation that goes with religious indoctrination.
So while my observations are strictly anecdotal and should be taken with a grain of salt, I do think there are some things the sociologists sometimes miss.
The Process of Deconversion
For most who leave religion, the process of deconversion is a long, slow process that takes months, years, or even decades to unfold. Most who are on the path do not know they are on the path until the journey is almost over. For many, the moment of realization consists of the realization "wait, I'm an atheist?"
The process for Christians generally involves a period of deep study of Christian theology, the origins of the Bible, and/or Christian apologetics. This generally comes before the moment of realization mentioned above. It can last for years and involves the believer desperately trying to prove to themselves that what they believe is true.
As they start to realize that it isn't true, they start to see how the Christian community behaves in shocking or immoral ways.
I've noticed a difference between the deconversion stories of older atheists (Generation X or older) versus the deconversion stories of younger atheists. With older atheists, the emphasis is on the question "Is Christianity true?" With younger atheists, the focus is more on "I no longer want to be associated with the immorality of Christianity."
That's not to say that younger atheists no longer engage in a years-long struggle with the truth involving intense study, nor does that mean that none of the older atheists were in part driven away by the immorality of Christians. It's just that among younger ex-Christians, the inciting incident is often the immorality of Christendom itself, whereas, with older atheists, the inciting incident is often wanting to prove to themselves (or someone else) that Christian beliefs are true.
It's not hard to understand why this shift is happening. In recent decades, white Evangelicals have radicalized to a shocking degree, and become much more overt in their immorality, while the Evangelicals I remember from my youth tried harder to hide their immorality from others.
In the past, bad truth claims drove people away from Christianity. People are leaving Christianity at a greater rate in America right now because Christianity in America is increasingly associated with immorality.
Demographic Shift Towards Liberalism
This is vaguely related, but if you talk to older atheists (such as Baby Boomer atheists), you find that atheists in the past were about equally likely to be liberal vs conservative. If you look at modern atheist groups, there is a definite trend towards liberalism, particularly as you move down in age towards the young.
I attribute this directly to the rise of radical far-right media such as FOX "News," and that army of right-wing AM radio hosts all across the country. The right-wing media openly appeals to white Evangelicals, and part of making themselves appealing to Evangelicals involved repeated attacks on atheists, which drove many atheists out of conservatism entirely.
As the right-wing media radicalizes the nation's conservatives, both the media and conservatives become more anti-atheist, more anti-science, more immoral, and more extreme in their views, all of which tend to drive atheists away from conservatism.
If you are a rightist and wonder why so few atheists, gays, racial minorities, etc. are in your movement, then maybe you should not spend so much time demonizing them. The people who tell you what to think deliberately drove those groups away in creating the very rhetoric that attracted you.
Reminder: It's About the Nones
While my focus on people leaving Christianity is those who leave Christianity to become atheists, it is worth remembering that the vast majority who leave Christendom join the ranks of the "nones," a group that includes atheists, but the majority of those leaving Christendom to become theist "nones."
This is a group that has long been a significant part of the American landscape but is ironically discussed among atheists more than among theists. Of course, atheists mention them to each other just to correct other atheists who look at the demographic changes and falsely believe that all of the "nones" are atheists. The vast majority of "nones" are theists of the "I believe in religion, just not organized religion" variety.
Given that theistic "nones" are much less vocal than other kinds of theists, it is easy to forget that they represent one of the largest faith groups in America today. Most of those leaving Christianity today end up in this category of theistic "nones."