Elsewhere: Prop. 8 witness criticized anti-gay measures Chron, Second Defense Witness Takes Stand in Prop 8 Trial KCBS, Same-Sex Marriage Case, Day 11: Churches Times, Gay-Marriage Foes Make Their Case WSJ, Controversial Tapes Shown in Prop 8 Trial KCBS, Brief disruption at #prop8 trial: pro-8 demonstrator gets public courtroom seat, yells “return the family 2 Jesus” is kicked out of courtand escorted out of Fed Bldg, ranting & screaming. First disruption in 11 days of #prop8 trial Douglas Sovern on Twitter, eHarmony settles lawsuit over gay matchmaking Chron, Prop. 8 witness warns of societal upheaval Chron

Previously: Prop 8 Trial, Day 11: Religion Critical Factor To Marriage Ban Passage

The final witness in a same-sex marriage trial testified in federal court in San Francisco today that he believes gay and lesbian marriage would weaken the institution, cause fewer heterosexuals to marry and possibly lead to polygamy.

David Blankenhorn, president of the New York-based Institute for American Values, also said children fare best when raised by a married man and woman who are their biological parents.

Blankenhorn, an author of books on marriage and fatherhood, was the second of two defense witnesses called by the sponsors of Proposition 8 in a trial on the constitutionality of the measure.

Proposition 8, enacted by state voters in 2008, requires marriage to be between a man and a woman.

Its sponsors, who are defending the initiative against a lawsuit filed by two same-sex couples, contend the measure is a reasonable way of preserving the traditional definition of marriage and promoting the well-being of children.

The plaintiffs in the case, a lesbian couple from Berkeley and a gay couple from Burbank, claim the ban on same-sex marriage violates their federal constitutional rights to due process and equal treatment.

Testimony in the two-and-one-half week trial before U.S. District Judge Vaughn Walker is expected to end at midday Wednesday with the completion of cross-examination of Blankenhorn.

Walker, who will decide the case without a jury, has said he will hear closing arguments at a later date after studying the evidence.

Under questioning from Proposition 8 lead attorney Charles Cooper, Blankenhorn testified, “The optimal environment for children is if they are raised from birth by their own natural mother who is married to their own natural father.”

He said the weakening or “deinstitutionalization” of marriage in recent decades was begun by heterosexuals, but said he feared that allowing same-sex marriage would accelerate the process and result in fewer heterosexual unions.

But during cross-examination by plaintiffs’ attorney David Boies, Blankenhorn wasn’t able to cite any experts who say that same-sex nuptials would lead to a lower rate of heterosexual marriage by deinstitutionalizing marriage.

Blankenhorn also acknowledged he wasn’t aware of any studies showing that children raised by same-sex couples have worse outcomes than those raised by heterosexuals.

In answer to another query from Boies, Blankenhorn said he thinks homosexuals and their children would benefit from gay marriage.

“I believe that adopting same-sex marriage would be likely to improve the well-being of gay and lesbian households and their children,” he told the court.

The Proposition 8 sponsors’ other defense witness, associate government professor Kenneth Miller of Claremont McKenna College, completed testimony this morning.

Miller testified on Monday that gays and lesbians in California are a powerful political force, with the ability to raise money in initiative campaigns and form alliances with political leaders, religious groups and unions.

His testimony was intended to refute the plaintiffs’ argument that gay rights are entitled to the highest level of legal protection because homosexuals lack political power and have historically suffered discrimination.

During Miller’s cross-examination this morning, Boies homed in on the claim that churches allied with gays in opposing Proposition 8.

The questioning was aimed at bolstering another plaintiff argument, a contention that the Proposition 8 campaign was illegally motivated by prejudice and moral disapproval of homosexuals.

Miller agreed that while some churches opposed Proposition 8, the state’s largest religious groups, including the Catholic Church and evangelical groups, supported the initiative and that the Mormon Church also played an important role.

He acknowledged he wrote in a scholarly article in 2009 that religion “was critical in determining voter attitude toward Proposition 8.”

Miller agreed that he wrote, “Churches and religious organizations supplied most of Proposition 8’s institutional support, with Catholics, Evangelicals and Mormons leading the way.”

In return questioning at the end of Miller’s testimony, Proposition 8 attorney David Thompson asked him to compare that initiative with other ballot measures that sought to limit gay rights.

Miller answered, “Marriage is a different situation and the people should be able to have input on the definition of marriage. It isn’t necessarily invidious discrimination against a minority group.”

Walker leaned over from the bench and asked whether it is ever appropriate for the judiciary to intervene in the initiative process.

Miller answered, “When there’s a well-grounded constitutional principle that is violated.”

The trial is the nation’s first in federal court on a challenge to a same-sex marriage ban under provisions of the U.S. Constitution.

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