With equal amounts enthusiasm and charm, Jeff Zarrillo and Paul Katami call themselves "regulars guys," and "loudmouths" to boot. Their once low-key love affair has put the couple from Burbank, California, in the national spotlight -- co-plaintiffs in a monumental fight now before the Supreme Court that tests the generations-old concept of marriage.

The same-sex couple wants to wed with the state's blessing and, along with a lesbian couple from Berkeley, they have challenged a voter-approved measure known as Proposition 8, which defines marriage only as between one man and one woman. Arguments in that and a related appeal over federal recognition of same-sex marriage will be argued next week.

But it is the "Prop 8" case where the high court is being asked to establish the constitutional "equal protection" right. It is the kind of hot-button issue that will define our society, our laws, our views on family.

"This is about our equality," Katami told CNN's Crime and Justice Correspondent Joe Johns. "This is about our freedom and our liberty. So we are not trying to topple marriage. We are not trying to redefine marriage. What we are trying to say is that equality is the backbone of our country."

"The biggest harm is probably that we can't get married and we love each other," added Zarrillo. "And the harm of not being able to call him my husband."

The political, social, and legal stakes of this long-simmering debate will once again put the high court at the center of national attention, a contentious encore to last summer's ruling upholding the massive health care reform law championed by President Barack Obama.

Forty-one states have specific laws blocking gays and lesbians from legally marrying. But last November, voters in three states -- Maryland, Washington, and Maine -- approved same-sex marriage, adding to the six states and the District of Columbia that already have done so. Minnesota voters rejected an effort to ban such unions through a constitutional amendment.

And just this week, elected leaders in New Mexico urged same-sex couples to apply for wedding licenses.

As more states legalize same-sex marriage, one of the key questions the justices may be forced to address is whether a national consensus now exists supporting the idea of expanding a "marriage equality" right to homosexuals.

There are about 120,000 legally married same-sex couples in the United States.

Nine other states, including California, New Jersey, Illinois, Delaware, Rhode Island and Hawaii, have legalized domestic partnerships and civil unions for such couples -- a step designed in most cases to provide the same rights of marriage under state law.

But other states have passed laws or state constitutional amendments specifically banning such marriages. California's Prop 8 is the only such referendum that revoked the right after lawmakers and the state courts previously allowed it.

Last year, a federal appeals court in San Francisco ruled the measure unconstitutional. In its split decision, the panel found that Proposition 8 "works a meaningful harm to gays and lesbians" by denying their right to civil marriage.

The law's supporters say a state's own citizens, not the courts, should decide such fundamental, time-honored questions.

"Marriage is the major cornerstone in Western civilization and that's how societies and cultures over time have defined it -- between one man and one woman. So, to suggest a transformation from that vital definition that's dramatically different is a very serious change that's upon us," said Austin Nimocks, co-counsel defending California's marriage amendment. He works at the conservative Alliance Defending Freedom. "But ultimately it depends whether Americans can make this decision for themselves and not have it imposed upon them by judges."

Dozens of civil rights and other gay rights groups are hoping the high court gives a sweeping endorsement of marriage equality for homosexual couples. The oddball legal team of conservative Theodore Olson and liberal David Boies successfully made their case in the lower courts and urged the justices to now order states to stop marriage discrimination on the basis of sexual orientation, calling it the "defining civil rights issue of our time."

"I think that we hurt people when we tell them they're no good. We tell them that they're not equal to us, and we say your loving relationship doesn't count?" Olson told CNN in 2010 as he argued the case in the federal appeals court. "We're putting a badge on them that says 'unequal' and that's contrary to everything we believe in this country."

Plaintiff: Who wants to celebrate a domestic partnership?

Katami is a fitness instructor, Zarrillo manages cineplexes. Fourteen years ago Jeff came out of the closet after moving to southern California. The two met online and their relationship has slowly developed into a lifetime bond.

They have never married, or had either a state-recognized civil union or domestic partnership, calling that "second-class citizenship."

"Marriage has distinctive definitions and rights that come with it. And a domestic partnership seems like a corporate document, in fact it acts almost exactly as one," said Katami. "Do you really invite people and have cake at a domestic partnership signing? That's not what represents who we are. We represent a married a couple and we need to be married."

They jumped into the political debate five years ago when Zarrillo saw an anti-gay marriage video online, called the "Gathering Storm." He encouraged his partner to see it.

"I was hounding him saying, 'Hey, did you watch the video?'" said Zarrillo. "And sure enough, when I finally got him to watch it, he stood up off the couch and he said we have to do something -- we can't allow this to stand. Then we decided to shoot a response video."

The YouTube video attracted hundreds of thousands of hits, and attracted the attention of gay rights groups planning a legal challenge.

Along with Kris Perry and Sandy Stier -- parents of four boys from the Bay Area -- the two couples agreed to put their names on an audacious lawsuit. They say gays and lesbians have a fundamental "equal protection" right to wed. They equate their cause to the civil rights struggles of a half-century ago.