A majority of voters stopped same-sex marriage in California simply by casting a ballot for Proposition 8.
This week, when a federal trial resumes in San Francisco, attorneys challenging Proposition 8 will continue building a multilayered argument that voters' action created an unconstitutional law based on prejudice and unfounded fear about homosexuality.
During the historic trial that began last week in U.S. District Court, attorneys for gay couples tried through opening arguments and witness testimony to show that the government - or the voters - have no rational purpose for excluding gays from a fundamental right such as marriage.
Proposition 8 attorneys, in an equally multifaceted approach, are working to establish that voters did have legitimate reasons to vote to make marriage only between a man and a woman.
"Same-sex marriage is simply too novel an experiment at this stage," and opposition to it doesn't necessarily spring from "ill will" toward gay people, Charles Cooper, one of Proposition 8's attorneys, argued last week in court.
Plaintiffs presented historians, plaintiffs and scholars of psychology whose testimony was intended to support the case for same-sex marriage rights.
Cambridge University psychology professor Michael Lamb testified that children in families with gay parents are no less well off than in families with heterosexual families.
Harvard historian Nancy Cott said interracial marriage prohibitions and legal limits on wives' rights were once defended as vital to the well-being of marriage and children.
George Chauncey, a Yale historian, described how unfounded accusations about gay people were used to justify, during various times in history, laws to purge gays from jobs and jail them. Proposition 8's messages, he said, echoed stereotypes used in the past to sow fear of gays.
The plaintiffs testified they felt anguish about a campaign they felt portrayed them as a danger to children. Scholars of psychology testified about the negative impact of gays feeling stigmatized.
"You can't deny a fundamental right without a good reason. You need a weighty reason," said Ralph Richard Banks, a Stanford Law School equal-protection law expert.
That's why the defense is highlighting voters' social concerns, and challengers are scrutinizing the tone of the Proposition 8 campaign, explained Calvin Massey, a constitutional expert at the University of San Francisco's Hastings College of the Law.
"Animosity is moral disapproval," Massey said. And moral disapproval can be shaky ground for barring someone from a right, he said.
This week, attorneys for the plaintiffs could try to bolster that argument by calling to the stand San Francisco resident William Tam, an ardent Proposition 8 supporter who asked to be a defendant in the trial.
Tam said in a Proposition 8 fundraising letter that gay marriage is part of an agenda to "legalize having sex with children," and that "other states would fall into Satan's hands" if same-sex marriage is not stopped in California.
The defense has yet to put on witnesses of its own. But it began through cross-examination to establish that voters were motivated by reasons other than prejudice.
In his opening remarks last week, defense attorney Cooper, a former Reagan administration lawyer, set the stage by declaring that procreation is a "defining" characteristic of marriage.
Defense lawyers said they were able to build their case by getting some witnesses to agree that parents have a right to decide what is appropriate for their children to learn, and that much of society does link marriage with heterosexual procreation.
The government, Cooper said, has an interest in steering child-rearing into mother-father unions. Before the trial is over, the defense plans to call its own witnesses to the stand to argue that children are ideally best brought up in that setting.
Proposition 8 attorney Andrew Pugno said his side doesn't have to prove that same-sex marriage will have an adverse impact on children or society.
The defense, he said, has only to make the case that society has legitimate concerns about same-sex marriage - which is relatively new - and that no one can prove it won't have a negative impact.
Banks said Pugno's contention that voters had rightful concerns about the unknown might be enough to win.
But it won't be enough, he said, if challengers persuade presiding Judge Vaughn Walker to make a historic legal conclusion about gay people.
Courts use three tiers of "scrutiny," Banks explained, to consider whether a law violates a person's constitutional rights. The lowest tier allows for a law only if there is a rational reason for restricting rights.
The second, intermediate tier is usually applied if a law commits gender discrimination. The highest tier of scrutiny tests if a law violates a person's rights based on racial or national origin.
"If you make a convincing enough case that gays and lesbians are vilified and wrongly stereotyped, valued less than others," Banks said, "then that could give the foundation for changing doctrine."
"The judge could say, 'I think it's time to recognize that gays deserve special protection just as other groups do,' " Banks said. "If the judge says it's time to embrace this new constitutional standard, then that would invalidate Proposition 8."
An appeal is expected at a higher court, no matter the outcome of this trial.