"The court is clearly nervous about constitutionalizing this issue. They were saying, 'We don’t know all the ramifications of this, so why not let different states experiment?'" he said. "If they say Proposition 8 is unconstitutional then they will effectively take away California's ability to take its part in that experiment."
Kennedy acknowledged the recentness of legalizing same-sex unions, a point stressed repeatedly by Charles Cooper, the lawyer for the defenders of Proposition 8. Cooper said the court should uphold the ban as a valid expression of the people's will and let the vigorous political debate over gay marriage continue.
But Kennedy also pressed him 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. The voice of those children is important in this case, don't you think?" Kennedy said.
Yet when Theodore Olson, the lawyer for two same-sex couples, urged the court to support such marriage rights everywhere, Kennedy said he feared such a ruling would push the court into "uncharted waters." Olson said that the court similarly ventured into the unknown in 1967 when it struck down bans on interracial marriage in 16 states.
Kennedy challenged the accuracy of that comment, noting that other countries had had interracial marriages for hundreds of years.
Several members of the court were troubled by the Obama administration's main contention that when states offer same-sex couples civil union rights of marriage, as California and eight other states do, they also must allow marriage. The other states are: Colorado, Delaware, Hawaii, Illinois, Nevada, New Jersey, Oregon and Rhode Island.
"So a state that has made considerable progress has to go all the way, but at least the government's position is, if the state has done absolutely nothing at all, then it can do as it will," Justice Ruth Bader Ginsburg said.
Chief Justice John Roberts questioned whether gay marriage proponents were arguing over a mere label. "Same-sex couples have every other right. It's just about the label," Roberts said.
Reflecting the high interest in this week's cases, the court released an audio recording of Tuesday's argument shortly after it concluded and plans to do the same Wednesday. The last time the court provided same-day audio recordings was during its consideration of Obama's health care law.
Same-sex marriage is legal in nine states and the District of Columbia. The states are Connecticut, Iowa, Maine, Maryland, Massachusetts, New Hampshire, New York, Vermont and Washington.
Thirty states ban same-sex marriage in their constitutions, while 10 states bar them under state laws. New Mexico law is silent on the issue but does not recognize same-sex marriage.
Polls have shown increasing support in the country for gay marriage. According to a Pew Research Center poll conducted in mid-March, 49 percent of Americans now favor allowing gays and lesbians to marry legally, with 44 percent opposed.
A significant part of the give-and-take Tuesday concerned Cooper's argument that the state has a legitimate interest in limiting marriage to heterosexuals since they have the unique ability to have children.
He and Justice Elena Kagan engaged in a lengthy, sometimes humorous, exchange on the topic.
“If a state can use the ability to have children as a reason to prohibit same-sex marriage, what about couples over the age of 55?” Kagan asked.
"Your Honor, even with respect to couples over the age of 55, it is very rare that both parties to the couple are infertile," Cooper said.
Kagan cut in: "I can just assure you, if both the woman and the man are over the age of 55, there are not a lot of children coming out of that marriage."
At another point, Justice Antonin Scalia, who has dissented in the court's previous gay rights cases, invoked the well-being of children to bolster Cooper's case.
"If you redefine marriage to include same-sex couples, you must permit adoption by same-sex couples, and there's considerable disagreement among sociologists as to what the consequences of raising a child in a single-sex family, whether that is harmful to the child or not," Scalia said.
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