The Supreme Court hears argument in a challenge to Prop 8 Tuesday.
Tony Perkins, president of the Family Research Council, told CBS's "Face the Nation" moderator Bob Schieffer opinion polls that suggest a majority of Americans now approve of gay marriage aren't the right indicator.
"The polls that really matter are the polls that are taken when the people actually vote on this," Perkins said. "And when people have voted, as late as 10 months ago, 30 states have put the natural definition of marriage into their state constitution, on average by a vote of 67 percent."
Perkins also assailed what he called an attack on "religious freedom" in the United States if gay marriage were to become the law of the land.
He also said of parents and business owners who don't want to be involved with gay couples getting married -- or have their children learn about them -- shouldn't be forced to do so.
"You have Catholic Charities no longer doing adoptions ... as a result of same-sex marriage in [Washington] D.C.," he said. "You have got parental rights that have been lost. Parents no longer determine -- being able to determine what their children are taught, whose moral values their taught in schools. We have small businessmen losing their rights because they won't participate in same-sex ceremonies."