Warning: Just a theory

Liberal Christian denominations (ie, Mainline Protestants) are caught in a paradox: even though they have increasingly defined themselves as open to everyone, their membership roles keep decreasing. It’s as if the more people they let in, the fewer people show up.
[insert Groucho Marx cartoon about not wanting to belong to the set of all clubs that would have him.]
Recent data from Minnesota highlights the precipitous decline:
Mainline Protestant churches have been hit the hardest. The Evangelical Lutheran Church in America (ELCA) in Minnesota has lost almost 200,000 members since 2000 and about 150 churches. A third of the remaining 1,050 churches have fewer than 50 members. The United Methodist Church, the second largest Protestant denomination in Minnesota, has shuttered 65 churches since 2000.
Catholic membership statewide has held steady, but the number of churches fell from 720 in 2000 to 639 last year, according to official Catholic directories.”
Note the timeframe: we’re not talking about change over the course of a century. The Presbyterian church of Minnesota has lost 42% of its members since 2000.
Meanwhile, membership is basically holding steady at conservative denominations that practically define themselves by whom they don’t let in. Evangelicals and fundamentalists are not hemorrhaging nearly as badly as their more welcoming brethren.
Among Mainline Protestants, the only denomination that’s basically holding steady is the American Baptist Church, which has gained black souls as it has lost white ones.
The African Methodist Episcopal Church has more than doubled in size.
Interestingly, a conservative spin-off of the Presbyterian church is doing fine, and the notorious Southern Baptists are doing fine. [source for denomination data.]
The Amish, who are practically their own ethnic group due to only marrying other Amish, have been nearly doubling their population every 20 years, and that’s even with a significant number of children leaving each generation. Of course, the Amish have plenty of children.
Of course, one of the biggest factors in the decline of liberal denominations is fertility–the Amish have a lot more kids than Mainline Protestants.
But why have the Mainlines, with their open and tolerant ideologies and welcoming attitude toward nearly everyone, not attracted more members as society in general has moved leftward on many issues? If you have read Dumbing of Age for as long as I have, then you are well aware of the main character, Joyce’s, rejection of the particular brand of conservative Christianity she was raised and homeschooled in over the issue of homosexuality, and her subsequent search for a more liberal church (which has so far involved freaking out at an Episcopalian service because it smacked of papistry.)
Why are Presbyterians failing to attract the Joyces of the world?
I propose this is because functionally religious identity is about group identity, and a group identity that hinges on “openness to outsiders” is not a functional group identity.
Now you might be saying, “Wait, I thought religious identity had to do with what you think God, or ethics, or how the world was created. People give some sort of rational thought to their beliefs, and then pick the church that best suits them.”
No. I don’t think anyone ever said, “Hey, the religion where you can’t eat pigs sounds much more rational than the religion where you can’t eat cows.” Nor did anyone logically think that the religions with animal sacrifice sounded more logical than the one where the feces of priests are holy, or where alien ghosts are causing all of your problems. (Basically, every religion that isn’t whatever you happen to practice is full of totally illogical beliefs.)
This is why conversations between atheists and theists are so boring. Atheists try to explain that religion doesn’t make sense, and theists try to explain that religion is about faith, not logic.
The nation of Pakistan is 96.4% Muslim, and it didn’t get that way because everyone in Pakistan spontaneously decided when they were about 16 years old that they all agreed that Islam was the only true religion. Israel is 74.7% Jewish, not because all of the Jews logically examined all of the world’s religion and then spontaneously agreed that Judaism was the best one. No; most of the world’s Muslims are Muslim because their parents were Muslim. Most of the world’s Jews were born to other Jews. Most Christians were born to Christians, and so on.
Multi-religious states exist, but within those states, people tend to marry within their own religion or abandon religion altogether, for religion is ethnicity.
3,000 years ago, this would have been an unexceptional statement. The People of the Crocodile God worshiped crocodiles and were certain those folks over there worshiped the Snake God were up to no good. Note that they didn’t deny the existence of the Snake God; they just didn’t worship it.
Our ancestral memetic environment was very different from our modern one because most people couldn’t travel far and mass media didn’t exist. As a result, people tended to only interact with their own group; outsiders were demonized and war was frequent. To be part of a tribe was to worship the tribe’s totems or ancestral deities. In an uncertain world where wind and rain, life and death were mysteries in the hands of capricious deities, to not worship the tribal gods was akin to saying you did not care whether your brothers lived or died.
Indeed, the big issue Rome had with Christians and Jews was less that they worshiped some strange god with weird food rules and transubstantiation–the empire had a pretty inclusive attitude of adopting new deities as it encountered them–but that Christians and Jews refused to adopt the empires deities into their pantheon. More to the point, they refused to sacrifice to the Roman gods, which the Romans believed would bring the wrath of the gods on them and showed very poor civic spirit. As Tertullian complained in the second century:
They think the Christians the cause of every public disaster, of every affliction with which the people are visited. If the Tiber rises as high as the city walls, if the Nile does not send its waters up over the fields, if the heavens give no rain, if there is an earthquake, if there is famine or pestilence, straightway the cry is, “Away with the Christians to the lions!
Monotheism of course triumphed over paganism by taking over the empire itself. The conquering of pagans and thus their gods happened on a small scale within Judea, then on a large scale with Rome and Mecca. The big religions now expanded past pure ethnic lines, but still functioned for ordinary people as ethnic identities due to the lack of long-distance travel–Christians, for example, were members of “Christendom,” which stood in contrast with the pagan, barbarian, and non-Christian hordes–places which, of course, the average christian never saw.
But modern technology has drastically changed our memetic environment. Today you can hop in a car or plane and within hours be hundreds or thousands of miles away–distances your ancestors would have taken months to walk. You can pick up your phone and talk to a friend on the other side of the planet, or read headlines detailing the spread of disease in a foreign country. (I have written extensively about this change in the memes category.)
In the ancestral memetic environment, almost everyone you talked to and got information from was either your immediate family or lived in your community. As a result, memes that promote the survival of you, your family, your community, and your genes tend to dominate. Memes that promote the survival of strangers don’t do as well.
In our modern memetic environment, most of the people you talk to and get information from are strangers. You get movie recommendations from strangers on Rotten Tomatoes; you learn about new business ideas from the reporters at Forbes or Wired or The Wall Street Journal; you get parenting advice from a nanny on TV and medical advice from WebMD. You no longer raise barns or herd goats with your brothers, cousins, and extended family, but work in a cubicle farm with a hundred people who probably aren’t even 5th cousins.
As a result, the modern memetic environment favors the horizontal (rather than vertical, ie from parent to child,) meme transfer. This environment favors the spread of memes that prioritize the interests of strangers, simply because so many of the people you are talking to and interacting with are strangers.
The liberal churches–in particular, the Mainline Protestants–have worked hard to signal openness to others, because this is how horizontal morality works. (The group identity of people who define themselves as open to others thus has as its group it’s defined against as “people who aren’t open to others.”) But if religion itself is about group identity, then a group identity of “let’s be open to others and not have a strong group identity” is going to leave people unenthusiastic about attending liberal churches.
Group identity used to be more intuitive for people, again, because they mostly interacted with members of their own group. Modern religious identity for most Christians is no longer explicitly ethnic (not if you want a place in polite society,) so the “outgroup” has switched gay people, who are such a small percent of the population (2-3%) that they’re effectively a symbolic issue for most parishioners. Unlike those dastardly followers of the Snake God, homosexuals have never made their own army, invaded a neighboring tribe’s territory, massacred all of the women and carried off the men.
(This is, in my opinion, a very silly rock to build one’s church on. Certainly churches for the first 1,900 years of Christianity didn’t make this a major, defining point of what makes them different from their competitors. Jesus himself didn’t say a whole lot about gay people.)
And getting back to fertility, people with stronger group identities–such as people whose religions tell them they should have a group identity and it is good to have a group identity that excludes those [evil outgroup people] tend to have more children, who are the literal future of the church.
Summary version: Religion is about group identity, but the modern memetic environment, ie liberalism, is anti-group identity. Churches that try to set themselves up in opposition to group identity therefore fail. But since ethnic identity is no longer in fashion, conservative religious groups now define themselves in opposition to homosexuals, a somewhat symbolic opposition considering that homosexuals have never constituted a military threat to anyone’s ethnic group.