Same-sex marriage, an on-and-off issue in election campaign seasons going back to the mid-1990s, is back with a vengeance for the 2010 cycle.

But, this time, it could play very differently—if Democrats and responsible Republicans choose to recognize the arguments for marriage equality that the judge of the Federal District Court in San Francisco outlined when he struck down California’s Proposition 8.

That’s not a pipe dream. It’s practical politics.

The decision by the judge to reject Proposition 8—the bar on marriage equality narrowly passed by the state’s voters in 2008—means that the issue is probably headed for the US Supreme Court. But, before it gets there, it will be dragged down the campaign trail once more.

Judge Vaughn Walker’s eloquent argument in the Proposition 8 case offers new language for defenders of the principle that this has always been a debate between those who favor protecting the basic human rights of all couples and families versus those who would discriminate based on their own fears and bigotries.

"Proposition 8 fails to advance any rational basis in singling out gay men and lesbians for denial of a marriage license," wrote Walker. "Indeed, the evidence shows Proposition 8 does nothing more than enshrine in the California Constitution the notion that opposite sex couples are superior to same-sex couples. Because California has no interest in discriminating against gay men and lesbians, and because Proposition 8 prevents California from fulfilling its constitutional obligation to provide marriages on an equal basis, the court concludes that Proposition 8 is unconstitutional."

There is simple logic in that statement, as there is in Walker’s rumination on why civil liberties cannot be put to a vote.

"Conjecture, speculation and fears are not enough," explained the judge. "Still less will the moral disapprobation of a group or class of citizens suffice, no matter how large the majority that shares that view. The evidence demonstrated beyond serious reckoning that Proposition 8 finds support only in such disapproval. As such, Proposition 8 is beyond the constitutional reach of the voters or their representatives."

These are just a few snippets from a very long ruling. But they are important because they offer candidates who are inclined to support same-sex marriage language that can and should be used in making the case that discrimination is wrong—even if a majority might choose to discriminate. It was wrong when Southern majorities discriminated against African-Americans. It was wrong when Southwestern majorities discriminated against Latinos. It was wrong when majorities in plains states and the West discriminated against Native Americans. It is just wrong. And it can and should be explained as such.

For too long, otherwise high-minded political players have allowed their responses to the debate over same-sex marriage to be defined by a fear that voters cannot be reasoned with on this issue.

That might have been true fifteen years ago.

But the time that has passed has not hardened positions. It has softened them. More Americans support same-sex marriage today than in the past, Solid majorities of young people favor removing all discriminatory barriers. And even among older Americans who are still uncomfortable with an expansive view of marriage, there are clear majorities in support of civil unions, domestic partnership registries and related initiatives to afford protections to same-sex couples.

The latest CBS/New York Times Poll on the issue—conducted in April of this year—asked: "Which comes closest to your view? Gay couples should be allowed to legally marry. OR, Gay couples should be allowed to form civil unions but not legally marry. OR, There should be no legal recognition of a gay couple’s relationship."

"Legal Marriage" won a plurality, with 39 percent, to 24 percent for "Civil Unions" and 30 percent for "No Legal Recognition."

Forced to choose beween allowing same-sex marriage and banning it, the split was 45 percent in favor of marriage equality and 53 percent opposed.

Those are national numbers. In some southern states, it is true that opposition to marriage equality remains daunting.

But in most of the rest of the country, the numbers are headed in the right direction. Or at least they are trending close enough to the margin of error to argue—not just morally but practically—for making a stand on principle.

This is not the time to run from a volatile social issue.

This is the time to seize the opening and make sincere, unapologetic and distinctly American arguments for fairness.

This is the time to state, bluntly, that discrimination is wrong and that it is at odds with the Constitution and with our best understanding of the phrase "equal protection under the law."

Avoiding the issue will not work.

Democrats and responsible Republicans should read Judge Walker’s ruling and recognize that it outlines a position that is worth fighting for—and that Americans are more likely now than ever before to embrace.

That’s the bet California Attorney General Jerry Brown has made. Brown, who is running again this year for governor, welcomed Walker’s decision.

"In striking down Proposition 8, Judge Walker came to the same conclusion I did when I declined to defend it: Proposition 8 violates the equal protection guarantee of the Fourteenth Amendment of the United States Constitution by taking away the right of same-sex couples to marry without a sufficient governmental interest," explained the former Democratic governor.

Brown’s no fool.

But his opponent, Republican billionaire Meg Whitman, is.

Whitman’s for discrimination, arguing that: "I believe marriage should be between a man and a woman."

So the lines are drawn in California. Brown is on the right side of the arc of history. Whitman is on the wrong side.

But this issue does not stop at the California state line. It will be in play in gubernatorial and congressional elections nationwide.

That prospect ought not be feared. Not any more.

Americans are ready to be reasoned with on this issue. They are ready for the right argument.

It is time to treat voters with respect and make that right argument, to say, "There is no rational basis for discriminating against same-sex couples. It goes against our best ideals and our best understanding of the values outlined in our founding documents."

That’s the only appropriate message morally—and, finally, it is the only smart message politically.