In 2002, the number of baptized US members of the Episcopal Church stood at 2.32 million. By 2012, that number had fallen to 1.89 million, a decline of 18.4 percent. Meanwhile, attendance has fallen even more steeply. Average Sunday attendance in its U.S. churches was 846,000 in 2002, but had fallen 24.4 percent by 2012 to only 640,000. Other signs of congregational liveliness have fallen even further. Baptisms have fallen by 39.6 percent, and marriages have fallen by 44.9 percent.

As for the ACNA? It's seen its membership rise by 13 percent and its Sunday attendance rise by 16 percent in the past five years. Since 2009, the ACNA has planted 488 new congregations. In 2012, the entire Episcopal Church managed to plant four new churches.

The Evangelical Lutheran Church of America

The Evangelical Lutheran Church of America (ELCA) was formed in 1987, when three Lutheran denominations merged to create the largest Lutheran church in America. For most of its history, gay men and women were permitted to be pastors, so long as they remained celibate. But in a narrow vote at its 2009 Churchwide Assembly, ordination was extended to gay men and women in "committed monogamous relationships." In addition, the Assembly passed an amendment allowing churches "to recognize, support and hold publicly accountable life-long, monogamous, same-gender relationships."

From ELCA's formation in 1987 to 2009, the average decrease in membership each year was only 0.62 percent. But after the liberalization of the ELCA's stance on sexuality, membership declined a whopping 5.95 percent in 2010 and 4.98 percent in 2011. Since 2009, more than 600 congregations abandoned the denomination, with almost two-thirds joining conservative Lutheran denominations like the North American Lutheran Church and Lutheran Congregations in Mission for Christ. By the end of 2012, ELCA had lost 12.3 percent of its members in three years--nearly 600,000 people. If the present rate of defections holds steady, ELCA will cease to exist in less than two decades.

The United Church of Christ

The United Church of Christ (UCC) has long had a reputation for unfettered liberalism, sometimes bordering on the radical. In 2008, for example, the pastor of the largest UCC congregations in the country was one Rev. Jeremiah Wright. The UCC's tendency for pushing traditional boundaries has led to unquestionably positive developments (such as the first African-American pastor as early as 1785) and the unquestionably silly (such as the first hymnal that refuses to call Jesus male). Needless to say, in 2005 UCC became the first U.S. mainline Protestant denomination to support same-sex marriage, and has been an outspoken voice in the gay marriage debate ever since.

While UCC has been bleeding members for decades, its decline rapidly acceleratedafter the gay marriage vote. Since 2005, UCC has lost 250,000 members, a decline of 20.4 percent over seven years. While an average of 39 congregations left UCC annually from 1990 to 2004, more than 350 congregations departed in the following three years. The UCC's own pension board called the 2000's decline "the worst decade among 25 reporting Protestant denominations," and admitted that "...the rate of decline is accelerating."

2013 marked a particularly grim milestone for the denomination, as membership finally fell below one million. If the post-2005 rate in membership losses doesn't taper out, the denomination will cease to exist in 30 years.

The Presbyterian Church U.S.A.

The Presbyterian Church U.S.A. (PCUSA) was flirting with loosening its sexual standards as early as its 2006 General Assembly, when it voted to allow ordination boards to essentially overlook clergy marriage standards if a candidate "adhere[s] to the essentials of the Reformed faith." By 2010, the General Assembly had passed an amendment to remove all clerical standards of sexual behavior entirely. This year's General Assembly voted overwhelmingly to change their Book of Order to redefine marriage as a civil contract between "two people" and to allow ministers to perform same-sex marriages where legal.

Hopefully by now, you can see where this is all headed. In 2006, 2.2 million people were members of PCUSA, a number that dropped 22.4 percent to 1.85 million by 2013. PCUSA's decline accelerated significantly after approving the ordination of non-celibate gay and lesbian clergy in mid-2011, which led to the creation of an alternative denomination in 2012 called ECO: A Covenant Order of Evangelical Presbyterians. Over 100,000 members left the PCUSA in 2012 alone.
Once again, if post-2006 trends continue, the denomination will cease to exist by 2037.

Meanwhile, in Conservative Churches...

The familiar answer from liberal mainline Christians is to protest that church attendance and religiosity is on the decline across-the-board, not just in denominations that embrace homosexuality. But this excuse fails to account for conservative denominations like the Assemblies of God, which has been consistently and rapidly growing for more than 40 years. Despite much of the hand-wringing over the Catholic Church's highly visible public advocacy against gay marriage, it has been consistently growing in the United States. Lord knows the Mormons haven't had any trouble growing. Even theologically conservative denominations that are declining, such as the Southern Baptist Convention, began declining much later and much less drastically than other denominations. The Southern Baptist Convention has only declined by 3 percent since its peak in 2007--an average of less than 1 percent annually--and has actually been adding congregations.

In the end, Christian supporters of gay marriage will likely view its effects on church membership as a side issue. Christians have a responsibility to grow their churches, but also a responsibility to promote what they believe is just in God's eyes. But for some strange reason, it seems like conservative Christians never have to sacrifice one responsibility to fulfill the other.

Alexander Griswold writes for IRD. The following article originally was published on The Federalist and is cross-posted here with permission