Now I'm going to try something unusual. I'm going to try to provide arguments for gay marriage addressing the point of view of the right -- first the social aspects and then the economic ones. I would appreciate hearing any well-reasoned arguments from the right that would counter what I present or input from the left that would supplement what I have here. I've intentionally left out fairness arguments, since I severely doubt that a fairness argument from one side will ever be found compelling by the opposing side on this issue.
Unnatural/sinful choice?
First off, granting social equality to homosexual relationships is not something the right is every going to be in favor of since they view homosexual acts as unnatural &/or against God's will and a matter of choice. Scientific evidence demonstrating that while individual acts involve choice, sexual orientation (attraction to same gender) is linked to genetics would help to soften the stance of some. Even if someone is opposed on the basis of morality, one can still view it as not the government's job to legislate morality but society's job to encourage morality through social pressure.
Corruption of youth?
Evidence suggests that sexual orientation is linked to genetics, so gay marriage is not going to make heterosexuals suddenly become attracted to people of their own gender. With or without gay marriage the social pressure to be "normal" will still suppress some homosexual activity. If someone's family, friends, and church are against homosexual relationships, then there will still be strong pressure for someone to live a heterosexual lifestyle. It should also be pointed out that the debate will not go away until gay marriage is legally accepted. Until that time gay rights activists will make sure that everyone knows of homosexuality and provide regular "shock therapy" to try to gain acceptance. The bigger the deal that is made of it, the more likely youth will experiment with homosexuality in order to rebel against authority -- especially since unlike drugs or alcohol that has no significant legal consequences. Also, homosexuals locked into gay marriages should be less likely to "lead youth astray" with chance encounters.
Promotes promiscuity?
Part of the right's opposition to gay marriage stems from their view (doesn't matter whether it is accurate or not) that homosexuality promotes a promiscuous lifestyle (viewed as wrong on its own and leading to transmission of disease). It should be pointed out that gay marriage would provide a legal structure that encourages close partnership in homosexual couples and reduces promiscuity. With less promiscuity there will also be reduced transmission of disease and less burden on the nation's health care system.
Link to pedophilia?
No study I have seen has shown a link between sexual orientation and likelihood to become a pedophile. However, let us consider if someone has suppressed strong sexual desires and eventually comes to the conclusion that only someone who is trusting and can be easily manipulated is a possible outlet for relief without getting caught. It would seem to me that having an acceptable outlet with a consenting adult would be preferable to imposing that sort of dilemma -- and the more stable the relationship, the less likely for pedophilic temptation to arise. Take the Catholic Church’s requirement that priests be celibate and their problem with pedophilic priests as an example.
Preservation of marriage and the family?
Gay marriage would expand, not reduce marriages. The only reason there'd be more divorces is because there would be more marriages. Allowing gay marriage would not change the vows that straight people make to each other. Children of a gay parent would be no worse off having their parent married to a same gendered person than just living with that person. The children may benefit from having a more stable environment due to the legal commitment of marriage, even if it is a "gay" one.
Increased burden on government services?
The right estimates 1-2% of people are homosexual. Gay rights organizations estimate that 5-10% are. Religioustolerance.org, which doesn't seem to have a particular agenda other than promoting understanding of opposing viewpoints, gives an estimate of 2-5%. If the right is correct, then at most we should see a 1-2% increase in marriage related government services. However, since gay couples rarely have children the net effect should be far lower as such services are more often than not tied to children. Most legal benefits of marriage are contractual conveniences that deal with things like inheritance and medical decisions and don't really have a cost to tax payers.
Shifting of tax burden?
Since most homosexual couples do not have children, they are more likely to both work. When both spouses work and have income that is not too far apart, currently they pay more taxes and not less. If the number of homosexuals is as the right says (1% to 2%), then the effect will be negligible. If the number is as gay activists say (up to 10%) then that probably means a modest tax windfall and shifting of tax burden from heterosexuals to homosexuals.
I believe the arguments above complete my slight shift from marginally against gay marriage to marginally for it. I still feel that redefining marriage on a national level is unrealistic at this time and a waste of effort in government. I also feel that it is not something that should be done without a lot of careful consideration. For the foreseeable future the definition of marriage is likely to remain a state issue, as it has been since the founding of the United States.