Boston ? Somewhere along the way, the dividing line over gay issues picked up and moved. It’s no longer between red and blue states, or left and right wings, but between nature and nurture. Or to be more precise, between those who believe that homosexuality is a choice and those who believe that homosexuality is innate.

Remember the moment in the 2004 debate when CBS’ Bob Schieffer asked Bush and Kerry whether they thought homosexuality was a choice? The president answered, “I don’t know,” and the senator replied, “We’re all God’s children.”

Well, it turns out that the more you believe homosexuality is innate, the more accepting you are of gay rights. A full 79 percent of people who think human beings are born with a sexual orientation support gay rights, including civil unions or marriage equality. But only 22 percent of those who believe homosexuality is a choice agree.

The same line can be found in the religious world between those who regard homosexuality as a (bad) choice and those who see it as (biological) trait. The most conservative Protestant churches that talk about the homosexual “lifestyle” prohibit gay ministers. Religious liberals who see sexual orientation as an inborn trait, are more open to gays in the pulpit.

All and all, Americans seem reluctant to condemn people for who they simply are.

What then do we make of the Catholic Church’s banning – and perhaps purging – of gay priests? On Tuesday, the much leaked and much awaited document from the Vatican said the church “cannot admit to the seminary or to Holy Orders those who practice homosexuality, present deep-seated homosexual tendencies or support the so-called gay culture.”

What was painful to many Catholics was the obvious scapegoating of gays for the church sexual abuse scandal. But there was something less obvious.

Thirty years ago the Catholic Church accepted the view that some were definitively gay. Church teachings said “they do not choose their homosexual condition.” Nevertheless, the new document doesn’t just ban gays who “practice” homosexuality, breaking the vows of celibacy. It bans all those with homosexual “tendencies.”

In the strange new backsliding language of the Vatican, homosexuality is a “tendency.” The church doesn’t define tendency, nor does it say whether such a tendency is biological. Voluntary or not, it marks a man permanently. As Matt Foreman, a gay activist raised Catholic, says, “Doesn’t matter what you do or believe or practice. If you are gay there is no making that better in the eyes of the church.”

Ironically, the only exemptions are offered to men who were not ‘real’ homosexuals but “transitory” ones. They’re given a pass, in the words of a Vatican cardinal, for “some curiosity during adolescence or accidental circumstances in a state of drunkenness or particular circumstances like someone who was in prison for many years.” A drunk or ex-con is OK; a chaste, gay seminarian is not.

The same cardinal said that banning gays from the priesthood was no more discriminatory than “if a person who suffers from vertigo is not admitted to a school for astronauts.” Such a dizzying analogy overlooks the fact that gay men are already among the stars of the priesthood.

The document does more than denigrate the priests who have given their lives to the ministry. In the face of a conflict between biology and sin, the church has labeled homosexuality as “intrinsically disordered.”

Let’s remember that the evidence is with those on the nature side of the dividing line. While we don’t know the precise biology, the weight of research suggests that sexual orientation is indeed something we are born with. Perhaps there is a “gay gene.” Perhaps the Japanese scientists who found how a gene alters the sexual orientation of the fruit fly will find a similar switch for people.

Science may well offer some future shocks. Imagine, for a moment, we could tweak the “gay gene” in a petri dish or a womb. What would the religious right, which opposes both homosexuality and embryonic research, say about eliminating the ‘sin’? What would the left, which favors reproductive choice but is appalled at the idea of “curing” a population of homosexuals, say?

For now, however, the church has run directly into a conflict. Increasingly, Americans accept homosexuality as something that isn’t chosen and cannot easily be changed. Meanwhile, the Catholic Church has moved in the opposite direction, rejecting men with “deep-seated tendencies.”

Once, even the most conservative and patronizing churches proclaimed they could love the sinner and hate the sin. The new pope’s Vatican has labeled homosexuals themselves as the sin. The case is closed and so are the doors to the seminary.