Why There Is No Religious Left

In short, because Leftists care more about leftism than religion:

You want to have gay sex? Be a female bishop? Change God's name to Sophia? Go ahead. The just-elected Episcopal presiding bishop, Katharine Jefferts Schori, is a one-woman combination of all these things, having voted for Robinson, blessed same-sex couples in her Nevada diocese, prayed to a female Jesus at the Columbus convention and invited former Newark, N.J., bishop John Shelby Spong, famous for denying Christ's divinity, to address her priests.

When a church doesn't take itself seriously, neither do its members. It is hard to believe that as recently as 1960, members of mainline churches — Episcopalians, Presbyterians, Methodists, Lutherans and the like — accounted for 40% of all American Protestants. Today, it's more like 12% (17 million out of 135 million). Some of the precipitous decline is due to lower birthrates among the generally blue-state mainliners, but it also is clear that millions of mainline adherents (and especially their children) have simply walked out of the pews never to return. According to the Hartford Institute for Religious Research, in 1965, there were 3.4 million Episcopalians; now, there are 2.3 million. The number of Presbyterians fell from 4.3 million in 1965 to 2.5 million today. Compare that with 16 million members reported by the Southern Baptists.

When your religion says "whatever" on doctrinal matters, regards Jesus as just another wise teacher, refuses on principle to evangelize and lets you do pretty much what you want, it's a short step to deciding that one of the things you don't want to do is get up on Sunday morning and go to church.

If you want to know how liberals have gutted mainline Protestantism, and why the LWM's myth of the "religious" Left is nonsense, read the whole thing.