(Jason Redmond ~ Associated Press)
The hearing before a three-judge panel of the 9th U.S. Circuit Court of Appeals also focused on whether supporters of voter-approved Proposition 8 have legal standing to challenge a lower court ruling that the ban was unconstitutional.
The judges did not issue an immediate ruling.
C-SPAN piped the nearly three-hour hearing into law schools, courthouses, community centers and elsewhere across the country, giving the public outside the courtroom its first -- and possibly last -- direct look at the debate raging in the federal case.
The U.S. Supreme Court blocked a lower court from broadcasting the full trial earlier this year, and the high court has a blanket ban on televising its own proceedings. That means the issue would be blacked out if it reaches the U.S. Supreme Court, as many legal experts and lawyers on both sides believe it will.
Matt Walker, 60, of Los Angeles watched the hearing with about 20 other people at the Los Angeles Gay and Lesbian Center in West Hollywood. He found the hearing to be fascinating.
"Nobody from either side was getting a pass. The judges asked very probing questions," he said.
Only a few people gathered at the San Francisco Lesbian, Gay, Bisexual and Transgender Community Center to watch the hearing.
"I feel like it's our civil rights issue of today," said Jubilee Menzies, a 33-year-old, who recently passed the state bar exam.
Viewers watched attorney Charles Cooper, who represents sponsors of the ban, argue that the state can treat same-sex couples differently when it comes to marriage without running afoul of the Constitution because "sexual relationships between men and women naturally produce children."
"Society has no particular interest in a platonic relationship between a man and a woman no matter how close it might be, or emotional relationships between other people as well, but when the relationship becomes a sexual one, society has a considerable interest in that," Cooper told the judges. "Its vital interests are actually threatened by the possibility of an unintentional and unwanted pregnancy."
Judge Stephen Reinhardt replied: "That sounds like a good argument for prohibiting divorce. But how does it relate to having two males and two females marry each other and raise children as they can in California and form a family unit where children have a happy, healthy home?"
Opponents of Proposition 8 contend it violates the due process and equal protection rights of gays and lesbians under the U.S. Constitution by denying them the right to marry the person of their choice and by singling them out for disparate treatment without a legitimate rationale.
Supporters of the ban succeeded in keeping the full trial earlier this year from being televised, saying they feared broadcasts could prompt violent extremists who support gay marriage to attack lawyers and witnesses who would be identified on TV.
The U.S. Supreme Court prohibited the broadcasts with a 5-4 ruling. The unsigned opinion also said U.S. District Court Judge Vaughn Walker, the trial judge, attempted to change the local court's rules barring broadcasts "at the eleventh hour to treat this case differently than other trials."
University of Pittsburgh law professor Arthur Hellman, who watched Monday's hearing in his office, said he understood the reluctance of the U.S. Supreme Court to allow television from its hearings.
The temptation for media to distort images or comments becomes greater with the high court than with lower courts that don't attract as much public attention, he said.
"I think it will be some time before the Supreme Court allows cameras," Hellman said.
In contrast, the 9th Circuit has allowed broadcasts of civil cases for years, and many state courts for decades have allowed broadcasts of high-profile cases such as the 1995 O.J. Simpson murder trial in Los Angeles, which became a ratings bonanza,
The California Supreme Court televises many of its oral arguments and twice aired the gay marriage debate when the issue came before it.
Thousands gathered in front of a large-screen television set up in a park across from San Francisco City Hall in March 2009 to watch a skeptical state Supreme Court grill gay marriage supporters over why it should invalidate California Proposition 8.
The state Supreme Court upheld the proposition later that year, which led to the federal lawsuit now under consideration before the 9th Circuit.
Associated Press writers Marcus Wohlsen in San Francisco and Christina Hoag in Los Angeles contributed to this report.