All it takes is a splash of cold water, just a bracing slap across the cheek, and the scales fall from their eyes. With that, opponents of same-sex marriage understand what the fuss is about: human dignity, equality, the longing for happiness.

The latest welcome convert is Republican Sen. Rob Portman of Ohio. The onetime supporter of the egregious Defense of Marriage Act and of a constitutional amendment to ban same-sex marriage, Portman is now a full-fledged supporter of gay marriage. Why the change of heart? He learned that his son is gay. The scales fell.

He has good company among conservatives. Former Vice President Dick Cheney, whose daughter is a lesbian, supports same-sex marriage. And while Portman is alone thus far among current Republican senators to renounce the hypocrisy of the Defense of Marriage Act, more than 100 Republicans are supporting the effort to overturn the amendment to the California constitution that banned same-sex marriage.

It is nothing short of stunning how quickly opinion has changed on same-sex marriage. Twenty-years ago, even the topic of homosexuality was spoken mainly in whispers. The change began with President Bill Clinton’s bid to open the military to gays and lesbians. It failed and produced the unfortunate “don’t ask, don’t tell” policy. But the barricade, already battered by millions of gays and lesbians who refused to live the lie that society demanded, was broken. Gay rights became mainstream news.

Even five years ago, though, it seemed all but impossible for same-sex marriage to become a mainstream issue. But it has. Americans have more and more come to understand that gays aren’t creatures from some netherworld, but their own sons and daughters, mothers and fathers, friends and neighbors and co-workers. For younger Americans, who are becoming a more influential component of the electorate, this just isn’t an issue.

That’s how it should be. Like left-handedness or green eyes, homosexuality is a normal variation of the human condition. And like left-handed or green-eyed Americans, gays and lesbians want to have the same rights as other Americans.

Those who continue to insist that homosexuality is a sin or a choice may never be convinced otherwise – at least, not until, like Portman, they are confronted with the cruelty of their position. But the world has changed; it is they who have to catch up. Gays and lesbians may now serve openly in the military. Same-sex marriage is hardly noticed today, thanks, in part, to the leadership of New York State, which legalized it in 2011.

It was Clinton who signed the Defense of Marriage Act in 1996. It was politically expedient and wrong, but was of its prejudiced time. So was the support of his successor, George W. Bush, for a constitutional amendment banning same-sex marriage. But now, following the lead of President Obama, who “evolved” last year into a supporter of same-sex marriage, Clinton has disavowed the Defense of Marriage Act, calling it what it plainly is: unconstitutional.

These events could hardly be occurring at a more favorable time. Next week, the U.S. Supreme Court is scheduled to hear arguments on the Defense of Marriage Act and California’s Proposition 8. The court should invalidate both for their failures to acknowledge what most of the rest of the country has already figured out: Gays are Americans, too.