Tom Farr is the director of the Religious Freedom Project at the Berkley Center for Religion, Peace and World Affairs at Georgetown University. He writes with Tim Shah in the New York Times:

In 2010, the U.S. District Court Judge Vaughn Walker invalidated a California ballot initiative for which millions of religiously motivated blacks and Latinos, among others, had voted on the same day they cast ballots for Barack Obama. The measure was Proposition 8, defining marriage as between a man and a woman. The presence of religious arguments in the campaign led Judge Walker to assert that the "moral and religious views" underpinning the vote were not “rational,” rendering the measure unconstitutional.

Walker's ruling, like Obama's assertion, represents a results-oriented effort to expel religious arguments from democratic deliberation. This has been a tempting device for partisans of all stripes. To silence religiously motivated civil rights advocates like Martin Luther King Jr., Jerry Falwell once asserted that “Preachers are not called to be politicians, but soul winners.” Whatever its source, any effort to confine religious people and their ideas to an innocuous spirituality or a merely ceremonial role in public life is a threat to religious liberty and to American democracy.