Here, I think, we come to a centrist position that has been missing in the polarized debate. Let me start with the common ground the mainline denominations already have. Homosexual orientation is not a sin. Homosexual practice is not a bar to membership in the church. On this both sides in the mainline church debate agree.
The Bible says homosexual practice is a sin. On this the conservatives are right. But some conservatives go way overboard in saying that it is among the worst of sins.
I think homosexuality is a sin like divorce, not a sin like sacrificing children to idols. The Bible strongly condemns divorce, and Jesus does so most of all. The Presbyterian Church had a significant debate about how to deal with the biblical condemnation of divorce, and changed its position in the middle of the last century. Divorce is no longer a bar to being a minister or elder.
The church did not change its teaching that divorce is a sin. Each divorce is a tragedy, to be regretted and repented of. But sometimes, the church concluded, it is the least-bad option available to a person or a couple. They are enjoined to repent, and sin no more. They may even remarry in the church, and serve in all its offices.
By making this pastoral accommodation to divorce, the church is not saying that divorce is a private matter, or just another lifestyle choice that is as good as any other. Some people may even be born with very difficult personalities, but I have never heard the argument that such people have a natural inclination to divorce, and therefore ought to act on their inclination.
I believe the church could accommodate homosexual practice in the same way that it has accommodated divorce, without abandoning its standards.
The church should promote and develop ways to help people work around their inclination to homosexual practice, just as the church promotes and develops many pastoral strategies to help people work around their inclination to divorce. The successful ministries that help people deal with their homosexual inclinations don't try to change peoples' orientations so much as help them to work around their inclinations successfully. This is much the way Alcoholics Anonymous helps alcoholics change their behavior, rather than trying to remake their whole orientation.
The church recognizes, though, that sometimes divorce is the least-bad alternative when a couple's attempt to practice marriage has failed. The church even goes so far as to sanction remarriages after divorce, in the hopes of helping to mend the broken. If all involved acknowledge that the best practice would be chastity and fidelity within the first marriage, the church can live with a good-enough second best of chastity and fidelity within a second marriage. In the same way, I believe, if all involved acknowledge that the best practice would be no homosexual practice, the church can live with a good-enough second best of chastity and fidelity within a marriage-like committed union.
It may appear that I am recommending a huge change in the church's position with this last point, but I am not really. The issue for the church has not been what precise sexual acts anyone is up to. In fact, the church really does not want to know the details of your sex life (and I certainly don't want to know). Instead, what the church has been concerned about all along is to have the biblical standards acknowledged as real standards. This means that we try to live within them, repent of lapses, and heartily endeavor to mend our ways. This is true of all sin, not just the sexual ones.
The issue is not whether the church can live with sinners, homosexual or otherwise. Everyone is a sinner. The whole church is made of sinners, including all of the church's officers. As a gay Unitarian minister I know put it, "The Bible has hundreds of passages against heterosexual sin, and six against homosexual sin. You wrestle with your hundreds, and I will wrestle with my six."
Let me take this argument out of the realm of the hypothetical. What I am arguing for is already the standard of most mainline Protestant denominations, including my own. The only part that has not been clarified is the last point – whether two homosexuals living together in a committed relationship can be good enough if they acknowledge that they should try to restrain their sexual practice. The acknowledgement of the church's standard, and repentance when we slip, is all that the church has asked of its officers.
This is a common ground we can reach.