These days, it's pretty hard to walk the streets of a California city without seeing same-sex couples -- shopping, strolling, holding hands, sometimes accompanied by children. What used to be called, self-consciously, "public displays of affection" are now merely public displays of ordinary family life. For gay folks, then, it is all the more stinging an irony that the one place where same-sex couples are invisible is in the advertising war over Proposition 8.

Proposition 8, of course, is the constitutional ballot initiative on whether to retain or reject same-sex marriage, which was legalized by the state Supreme Court in May. Given California's power to shape national trends, the stakes for both sides could not be much higher. But given the sheer size of the state's media market, TV advertising could not be much more expensive. For both sides, the premium is on common-denominator messaging that appeals to the largest possible number of swing voters while causing a minimum of political backlash.

The need to walk that tightrope helps explain why the actual subjects of next month's initiative, gay couples, were "inned" by the "No on 8" campaign's ads. (Full disclosure: I am a "No on 8" donor.) One ad, for example, features a gray-haired straight couple. "Our gay daughter and thousands of our fellow Californians will lose the right to marry," says mother Julia Thoron.

A subsequent ad, all text with voice-over narration, mentions marriage only once ("Regardless of how you feel about marriage, it's wrong to treat people differently under the law") and never uses the phrase "gay marriage" or even the word "gay." Just as oblique was a spot, released Wednesday, in which state Supt. of Public Instruction Jack O'Connell reassures viewers that "Prop. 8 has nothing to do with schools or kids. Our schools aren't required to teach anything about marriage." A casual viewer could have come away from these ads puzzled as to exactly what right thousands of Californians might be about to lose.

Asked about the absence of gay couples, a senior "No on 8" official told KPIX-TV in San Francisco that "from all the knowledge that we have and research that we have, [those] are not the best images to move people." Children, also, were missing; showing kids with same-sex parents could too easily backfire.

The pro-Proposition 8 forces, by contrast, featured a child prominently in their TV advertising: A schoolgirl comes home with a book called "King and King" and announces, to her mother's consternation, that she learned in school that "I can marry a princess." Another ad attacks overweening judges, mocks San Francisco Mayor Gavin Newsom for saying, "It's going to happen whether you like it or not," and goes on to claim that gay marriage could cause people to be sued for their beliefs and churches to lose their tax exemption.

Notice, again, that gay couples were missing, though for a different reason. Nowadays, swing voters are more leery of anti-gay discrimination than of same-sex couples. So the "yes" ads changed the subject, focusing on alleged (and disputed) follow-on effects of same-sex marriage rather than on the thing itself. If homosexuals can get married, look what else might happen! Arrogant judges, politicians and school bureaucrats will harass churches, torment dissenters and inappropriately sexualize education!

Whatever the tactical considerations, the absence of gay couples and gay marriages from California's gay-marriage debate makes for an oddly hollow discussion. It leaves voters of good conscience to conjure in their own minds the ads that are not being aired: Ads that show how gay marriage directly affects the couples and communities that need it most.

What might such ads show? Well, one might feature someone like my friend Brian, who married his partner, Doug, on Saturday. They already had a domestic partnership, but that could not begin to match the power of marriage, sealed before parents and friends in a ceremony in San Francisco. "It's how you say this is forever and do it publicly," Brian says. "It's very different from getting a form notarized at Mailboxes Etc."

An ad might show Brian driving Doug to the hospital and sitting at his bedside after surgery. Marriage is unique because of the high social expectations that go with it. Chief among those expectations is that spouses will do whatever is necessary to care for each other -- which is valuable, because census data show that almost a third of California's gay couples have only one wage-earner, and almost a fifth have at least one disabled partner (about the same, by the way, as for straight married couples). By supporting and reinforcing the care-giving commitment, each marriage, gay no less than straight, creates social capital for the whole community.

Brian and Doug don't have kids, but a fourth of California's gay couples do, according to census data. An ad might show some of those kids watching as their parents, previously denied marriage, tie the knot. For children, no other arrangement matches the security and stability afforded by married parents, because no other arrangement confers comparable status and social support. If they could cast ballots, how many of the more than 50,000 children being raised in California's same-sex households would vote to deprive themselves of married parents?

Or an ad might feature a gay teenager celebrating his parents' 20th wedding anniversary and dreaming of his own someday. There are countless gay youths for whom the prospect of marriage will be so much more tangible if it is embraced by the nation's largest state. The breakthrough effect of same-sex marriage is not on the mature gay couples who can finally get marriage licenses, important though that is; it is the effect on generations of gay kids who will no longer grow up assuming that their love must separate them from life's most essential institution.

Keeping marriage available to gay couples in California, and giving it the blessings of a popular majority, would be a game-changer for gay culture. It would signal that the transformation from a pariah culture in the 1950s, to a promiscuity culture in the 1970s, and then to a commitment culture in the AIDS era and beyond, has taken its last and greatest step: to a culture of family.

Ellen DeGeneres, the comedian and TV personality, made an unofficial anti-Proposition 8 ad calling her marriage "the happiest day of my life." For the most part, however, you have seen and heard least about those who benefit most from gay marriage. That does not mean, however, you shouldn't think about them.

Jonathan Rauch is a guest scholar at the Brookings Institution and author of "Gay Marriage: Why It Is Good for Gays, Good for Straights, and Good for America."