Should Christians Quote the Old Testament to Oppose Gay Marriage?

In response to an earlier post asking if gay marriage is an economic issue, a former student sent me a link to the clip from an episode of The West Wing in which the President responds to a radio host who quotes the Old Testament to denounce homosexuality as an abomination.

A Wikipedia episode description says:

In its second season episode "The Midterms", President Bartlet admonishes fictional radio host Dr. Jenna Jacobs for her views regarding homosexuality at a private gathering at the White House. Dr. Jacobs is a caricature of radio personality Dr. Laura Schlessinger, who strongly disapproves of homosexuality. Many of the president's biblical references in his comments to Dr. Jacobs appear to have come from an open letter to Dr. Schlessinger, circulated online in early May 2000.

Is it fair and reasonable for Christians to cite parts of the Old Testament as justification for beliefs while ignoring other parts? Do the messages of love, compassion, and forgiveness in the New Testament contradict the vengefulness of the Old Testament?

Is Opposition to Gay Marriage an Economic Issue?

The chairman of the Republican National Committee, Michael Steele, recently provided an economic argument for the opposition to gay marriage:

"Republicans can reach a broader base by recasting gay marriage as an issue that could dent pocketbooks as small businesses spend more on health care and other benefits, GOP Chairman Michael Steele said Saturday.
Steele said that was just an example of how the party can retool its message to appeal to young voters and minorities without sacrificing core conservative principles. Steele said he used the argument weeks ago while chatting on a flight with a college student who described herself as fiscally conservative but socially liberal on issues like gay marriage.

`Now all of a sudden I've got someone who wasn't a spouse before, that I had no responsibility for, who is now getting claimed as a spouse that I now have financial responsibility for," Steele told Republicans at the state convention in traditionally conservative Georgia. "So how do I pay for that? Who pays for that? You just cost me money.´"

Regardless of one´s position in the gay marriage debate, is this the type of reasoning that should decide this issue? The same logic can be applied to the advocacy of almost any prejudice or bigotry. For example, does Michael Steele want to deny equal pay for women? Is the Republican Party opposed to paying women the same wages and salaries as men for doing the same job because it will be more costly to businesses? Would the GOP advocate a law that requires businesses to pay women less than men? It would save small businesses money, would it not?

Or how about other discriminations, such as on the basis of race or religion? Does the Republican Party advocate maintaining spousal benefits for white Protestants, but abolishing them for blacks, Hispanics, Asians, Catholics, Jews, and Muslims? Those actions would save small businesses money. Yet, that does not make it the right thing to do.

Or perhaps Michael Steele wants Republicans to advocate the general abolition of marriage. Not providing spousal benefits for anyone would reduce business expenses, right?