The message from Tuesday's Sioux City, Iowa anti-gay marriage rally was repeal.

About 50 people gather in a parking lot where the National Organization for Marriage (NOM) had parked its Summer for Marriage Tour 2010 bus.

The nation's most vociferous opponent of gay marriage has mounted a 23-city bus tour to promote marriage as between “one man, one woman.” The tour is expected to end with a Washington D.C. rally on August 15.

Iowa became the first – and remains the only – Midwestern state to legalize gay marriage when the Iowa Supreme Court unanimously ruled in favor of advocates last year. The issue is driving many of the state's top races, with several Republicans openly campaigning in favor of a constitutional amendment to define marriage as a heterosexual union.

Several attempts to begin the amendment process have been blocked by Democratic leaders in the Legislature, angering social conservatives opposed to the institution.

At a Sunday rally in the capital of Des Moines, Tamara Scott, director of the Iowa chapter of Concerned Women for America, framed the gay marriage debate in terms of dollars and cents.

“It costs you, the taxpayer, as high as $280 billion a year for fragmented families, according to the Family Research Council,” Scott told the crowd, referring to a 2009 study from the social conservative group.

“If we would correct the breakdown of the family by 1 percent, we could save the taxpayer $3 billion a year. … We can fix this economic downturn very easily by fixing some hearts,” she added.

Studies by the Williams Institute at the UCLA School of Law, however, show that gay marriage has been a boom for states that have legalized it. A 2008 study estimated that the institution would generate $160 million for Iowa through 2011.

At a pro-gay marriage event held two miles down the road, First Lady Mari Culver told the Iowa Independent that she disagreed with Scott's views of how gay marriage impacts the economy.

“I think [NOM] is looking for some economic cover, rather than reveal that some in their group are simply anti-gay,” she said.

In Sioux City, speakers pounded away at the theme of abolishing gay marriage in Iowa.

“The justices have been like black robed bandits while legislating from the bench. 'We the people' – it is our obligation to act,” Scott told the crowd

Danny Carroll, a former Republican legislator and chairman of the Iowa Family Policy Center, reminded the crowd to vote for anti-gay marriage candidates, including several justices up for re-election.

“Legislators are counting on people to forget about what they did with marriage,” Carroll said. “The power of democracy is with you the people. Find out where your legislators stand. Look them eye to eye and ask them directly. They are public servants – they work for you.”

“Many Iowans plan to vote NO on the justices being retained – holding them responsible for what they've done to marriage. It is time to say enough is enough!”

And NOM President Brian Brown reminded the crowd that his group had successfully campaigned for passage of Proposition 8, the 2008 measure that ended gay marriage in California after the state Supreme Court legalized it.

“If things look tough in Iowa with the Supreme Court, look at California two years ago,” he said.

Gay marriage advocates kept their distance in Iowa. In Sioux City, an estimated sixty-four people joined the state's largest gay advocate, One Iowa, at a nearby counter demonstration.

One Iowa recently announced that 2,500 gay and lesbian couples have married in the state since the law came into effect.

The bus rolls into Clayton, Missouri on Thursday.