"We're Americans who happen to be gay. That shouldn't invalidate our inalienable rights," said Jeff Zarillo and Paul Katami of Burbank, one out of two couples named in the lawsuit before the Supreme Court.
Represented by their lawyers, Katami and Zarillo challenged the voter-approved ban, stating the Constitution guarantees equal protection under the law and that marriage is a fundamental right.
Their lawyers urged the justices to strike down not just the California provision, but constitutional amendments and statutes in every state that define marriage as the union of a man and a woman.
"From the beginning, this case has been about securing the right for me to marry the person that I love," Katami said, "and also having the equal access to the most important relationship that I know in life, and that's marriage."
Proposition 8 advocates' main argument was the biological difference between same-sex and opposite sex marriages. Supporters of Prop. 8 also stressed that the court should respect the verdict of California voters who approved the ban in 2008 and let the fast-changing politics of gay marriage evolve on their own, through ballot measures and legislative action, not judicial decrees.
"We believe that Prop. 8 is constitutional," said Charles Cooper, an attorney for petitioners. "The place for the decision to be made regarding redefining marriage is with the people, not with the courts."
The nine justices questioned lawyers from both sides in the hearing. There was no majority apparent for any particular outcome. Several justices, including some liberals who seemed open to gay marriage, raised doubts during the riveting 80-minute argument before them.
A skeptical Justice Samuel Alito cautioned against a broad ruling in favor of gay marriage precisely because the issue is so new.
"You want us to step in and render a decision based on an assessment of the effects of this institution which is newer than cellphones or the Internet? I mean, we do not have the ability to see the future," Alito said.
Justice Anthony Kennedy, who many believe is the swing vote, said he feared the court would go into "uncharted waters" if it embraced arguments advanced by gay marriage supporters.
Kennedy pressed the lawyer for the defenders of Prop. 8 to address the interests of the estimated 40,000 children in California who have same-sex parents.
"They want their parents to have full recognition and full status," Kennedy said. "The voice of those children is important in this case, don't you think?"
The court could uphold Prop. 8 or strike it down and apply a broad ruling invalidating gay marriage bans in roughly 40 states. But the justices could also issue a ruling that applies only to California or to the nine states that allow domestic partnerships.
Same-sex marriages advocates and opponents made their sides heard ahead of Tuesday's historic hearing in Washington. Both sides of the case were represented outside the courthouse as big crowds camped out since Thursday to witness the event. Supporters of gay marriage came with homemade signs, including ones that read "a more perfect union" and "love is love." Opponents held signs that said, "Every child deserves a mom and dad."
"It's almost impossible to wrap your mind around the enormity of what's going on today," said actor-director Rob Reiner, who helped lead the fight against California's Prop. 8. "This ultimately will be the last piece of the civil rights puzzle being put into place."
Opponents of Prop. 8 in California organized rallies, marches and vigils to voice their opinions that same-sex marriages should be allowed in the Golden State.
Hundreds of same-sex marriage supporters marched from San Francisco's Castro District to City Hall on Monday. It was the largest march in the area in years.
Locally, the debate has ignited emotions throughout the Southland, primarily in West Hollywood and Long Beach, which have been leaders in the fight for same-sex marriage.
Long Beach Mayor Bob Foster raised an LGBT pride flag over the City Hall plaza in support of gay marriage Tuesday as part of the Courage Campaign's California Mayors United Against Proposition 8 movement. The rainbow flag will fly over the plaza for the next two days while the justices continue to argue the constitutionality of same-sex marriage.
Dozens of people attended a candlelight vigil outside Long Beach City Hall at sunset.
"We're all here hoping and praying they make the right decision," said Randy Salinas of Long Beach.
The court will hear arguments Wednesday on the 1996 federal Defense of Marriage Act, which forbids the recognition of same-sex marriages nationwide and bars married gay and lesbian couples from receiving federal benefits.
The court's eventual ruling is not expected before late June.
Kevin O'Grady, the executive director of the Gay and Lesbian Community Services Center of Orange County, calls this an anxious time for the LGBT community.
"There are literally millions of people for whom this is the civil rights decision of their lives," said O'Grady, who married his partner during the brief window when same-sex couples could marry in California.
In an exclusive Eyewitness News poll conducted by SurveyUSA, California respondents were asked whether their opinion on same-sex marriage has changed or remained the same over the past couple of years. Seventy-nine percent said their opinion has remained the same, 17 percent said it has changed and 4 percent said they were not sure.
"My gut says that we'll have to be back one more time to ultimately manifest the adjudication for all 50 states, based on what I heard, but that's just a pundit talking," said California Lt. Gov. Gavin Newsom, who was at the high court for the hearing.
The Associated Press contributed to this report.