A judge overturns a ban on same-sex marriage in the U.S. state of Michigan, the latest in a series of rulings across the country. (Reuters)

A federal judge Friday struck down Michigan’s ban on same-sex marriage, saying the state failed during a two-week trial to justify a prohibition that he said violates the equal protection rights of gays.

U.S. District Judge Bernard A. Friedman dismissed the state’s contention that Michigan voters adopted the ban on the premise that heterosexual married couples provided the optimal environment for raising children.

There is no proof that such a premise is true, Friedman wrote, and he declared the testimony of the state’s main witness “entirely unbelievable and not worthy of serious consideration.”

Unlike judges who recently struck down bans in other states, Friedman did not stay his decision, which could set off a rush of marriages by same-sex couples.

But his decision was issued late Friday afternoon as clerk’s offices were closing. Michigan Attorney General Bill Schuette (R) immediately appealed the decision to the U.S. Court of Appeals for the 6th Circuit and asked for a stay. A county clerk in Ann Arbor announced Friday night that he would open his office Saturday morning to allow couples to marry if a stay has not been issued.

Same-sex marriage status in the U.S., state-by-state

“In 2004 the citizens of Michigan recognized that diversity in parenting is best for kids and families because moms and dads are not interchangeable,” Schuette said in a statement. “Michigan voters enshrined that decision in our state constitution, and their will should stand and be respected. I will continue to carry out my duty to protect and defend the constitution.

Friedman, 70, who was appointed by President Ronald Reagan and took senior status in 2009, said the state’s defense of the law was misguided. “In attempting to define this case as a challenge to ‘the will of the people,’ state defendants lost sight of what this case is truly about: people.”

Like other federal judges in Virginia, Oklahoma, Texas and Utah who have struck state bans, Friedman relied on two Supreme Court precedents: Loving v. Virginia, which invalidated state bans on interracial marriage in 1969, and last June’s U.S. v. Windsor, which overturned part of the Defense of Marriage Act withholding federal benefits from same-sex couples married in states where such unions are legal.

Unlike those judges, Friedman conducted a trial. In his 31-page decision, he said he gave great weight to studies presented by lawyers for the plaintiffs, lesbian couple April DeBoer and Jayne Rowse, who have been together for eight years and have three children, whom they cannot jointly adopt.

Those studies, Friedman said, showed there was no dis­cern­ible difference in parenting competence between gay couples and heterosexual ones.

By contrast, Friedman was scornful of a state witness, University of Texas sociologist Mark Regnerus. Friedman said Regnerus’s study — which suggested children of those in same-sex relationships fared poorly — was shoddy and intended to please the anti-gay activists who had funded it.

“The funder clearly wanted a certain result, and Regnerus obliged,” Friedman wrote.

Friedman’s decision continued an unbroken string of success in the federal courts for same-sex marriage activists, following the Windsor decision. The rulings, which include three that require recognition of such unions conducted in the 17 states and District of Columbia where they are legal, are now on appeal.