In court, the Prop. 8 Proponents had little evidence to justify the discrimination imposed by Prop. 8. One of their main arguments during the 2010 trial centered on their assertion that being gay is a choice. If people can change their sexual orientation, they claimed, then there is no need to extend the right to marry to gay and lesbian Americans. (Flawed logic for the people who are happy and content with being gay, for sure.)

On the final two days of trial, the anti-marriage proponents of Proposition 8 called David Blankenhorn to testify about marriage and the family.

The proponents of Proposition 8 called Kenneth Miller, a professor of political science at Claremont McKenna College, as an expert in American and California politics.

On the ninth day of trial, Gregory Herek, a professor of psychology at the University of California, Davis, testified about sexual orientation and social stigma.

Hak-Shing William Tam, an official proponent of Proposition 8, was called as an adverse witness by plaintiffs. He testified about the messages he disseminated during the Proposition 8 campaign.

Stanford political science professor Gary Segura testified about the political powerlessness of gays and lesbians in the United States.

On the seventh day of trial, Ryan Kendall testified about his experience as a teenager whose parents placed him in therapy to change his sexual orientation from gay to straight.

Mayor Jerry Sanders of San Diego, a Republican, testified about how he came to support marriage equality.

On the sixth day of the trial, University of Massachusetts Amherst economics professor M.V. Lee Badgett testified about economic and demographic issues related the gay and lesbian couples and their children.

Psychologist Michael Lamb testified as an expert on the developmental psychology of children, including the developmental psychology of children raised by gay and lesbian parents.