These days, Californians may be forgiven for feeling as though they are playing host to a dinner party whose guests keep arguing in nastier and nastier terms.

Proposition 8 -- the statewide initiative that seeks to add a ban on same-sex marriages to the California constitution, reversing this spring's court decision legalizing such unions -- has turned into a bitter and expensive campaign, even by this sate's standards. Money has been pouring in on both sides of the issue, from churches, businesses and human rights groups around the country. With more than $60 million raised for and against the initiative, contributions to Prop 8 already exceed the combined total of all donations in the 22 previous campaigns over gay marriage measures in other states around the country.

The outcome is very much in doubt, with polls showing a tight race. But even if supporters of same-sex marriage manage to defeat Prop 8 and preserve the legality of such marriages here, their campaign against Prop 8 may eventually be considered something of a setback for the cause of marriage equality.

Why? The No on 8 campaign has been a strategic disaster, squandering the considerable political momentum that same-sex marriage had here. TV ads have been unfocused and confusing, and the far more disciplined Yes on 8 campaign has dominated the narrative in the newspapers and other media. The No campaign recently brought in new public relations and media consultants in the kind of last-minute shake-up that is characteristic of floundering campaigns.

Despite numerous advantages -- the court ruling this spring legalizing gay marriage, triumphant media reports on the thousands of couples who have held wedding ceremonies in recent months -- surveys now show public opinion moving in favor of the ban.

So, in these desperate final weeks, the new campaign team for No on 8 has adopted a tough, closing message that may yet salvage victory for same-sex marriage. The message? The people behind the ban are Mormons.

This a high-risk move, despite the message's accuracy. The Church of Jesus Christ of Latter-day Saints, better known as the Mormon church, has made unusually direct appeals to its members nationwide to support Prop 8 with their time, money or both. And Mormons have responded. By various estimates, somewhere between one-third and one-half of the approximately $30 million in donations in favor of Prop 8 has come from members of the church.

This Mormon support is so vast that it's a political vulnerability for the Yes on Prop 8 campaign. In polls, Americans register a low opinion of the Mormon religion (In a 2007 CBS News survey, the religion had a 25 percent favorable rating; the only faith less popular was Islam).The church's history on marriage -- it ended polygamy in 1890 -- is a complicated one. So Mormons are a tempting target. But by raising the issue of Mormon support for the ban, supporters of same-sex marriage, who have spent decades battling religious prejudice, are now in the awkward position of profiting from religious prejudice.

There is rough justice in that. Perhaps too rough. It's unlikely that the progressive groups would ever single out their political opponents' religion if the religion in question was Judaism or Catholicism. But they haven't hesitated in making an issue of the Mormon connection: No on 8 petitions circulated by progressive organizations demand that Mormons retreat from their support of Prop 8, and the executive director of the Ballot Initiative Strategy Center, which backs progressives in ballot initiative campaigns, has used the Huffington Post to frame the election in religious terms: "Do you believe the Mormon church shares your values on marriage or do you believe the constitution should treat everyone equally?"

At the extreme, the "Kossacks" at Daily Kos are compiling a list of Mormon donors to the Prop 8 campaign and urging people to send in damaging information about individual Mormons that can be used against the Yes on 8 effort.

In defending such tactics, supporters of same-sex marriage invoke an eye-for-an-eye logic, and not without justification. The Yes on 8 campaign has been cynically skillful in changing the subject from whether gays deserve marriage equality to more highly charged questions. Will churches be sued for refusing to marry gay couples? Or will young children have to be taught about same-sex marriage in schools? Both claims, advanced in Yes on 8 ads, have little basis in fact. California education leaders have been particularly adamant in refuting the latter. But these denials have served the purposes of the Yes on 8 campaign by focusing attention on schools and churches rather than on the needs of gay couples.

In its final days, the campaign in California feels less like a debate over the nature of marriage and more like a low-down discussion of which is creepier: gay sex or Mormons?

The No on 8 campaign may well prevail in that argument, and a win is usually a win in politics. But that's not true when it comes to advancing a controversial change in a major social institution. An ugly victory in California under such circumstances doesn't provide much of a foundation to advance same-sex marriage rights in the rest of the country.

Supporters of same sex marriage need to remember that marriage equality can't be won in one state. Federal law prohibits U.S. government recognition of same-sex marriage so even gay couples legally married here don't have the full rights of opposite-sex married couples. Those of us who favor same-sex marriage must keep our eye on the ball: the rapid expansion of same-sex marriage to all states and the repeal of the federal ban.

To accomplish that, same-sex marriage supporters need to build broad consensus in favor of such marriages. In the process, they must be careful not to harden opposition to the point that same-sex marriage becomes a perennial wedge issue like abortion. Same-sex marriage supporters need to convince a broad swath of religious voters that gay marriage deserves respect or that, at the very least, such unions pose no threat to their faith. But it's hard to make that argument when same-sex marriage supporters are making an issue of the religious affiliations of their opponents.

The movement for marriage equality should adopt a rule of never speaking ill of anyone on religious grounds. When confronting appeals to anti-gay bigotry, same-sex marriage supporters need to resist responding in kind. Call it the "turn the other cheek" method. Or to put it another way: when it comes to dealing with intolerance towards gay couples, the wisest long-term political strategy may be: hate the sin, love the sinner.