This is the best address to this issue I've heard yet. I /highly/ suggest listening to it, no matter what side of this issue one is on ...
Dennis Prager: Defending Marriage
http://www.family.org/fmedia/broadcast/a0032425.cfm
Or here ...
http://www.oneplace.com/Ministries/Focus_on_the_Family/Default.asp
For those without the audio accessibilty, here is a summary of Mr. Prager's comments (from http://www.family.org/ )...
* Avoid the "gays are born that way" argument. It's irrelevant to the question of whom we marry.
* "'Studies show' is the mantra of those who don't think," Prager says. Avoid the oft-used phrase, and beware that data can be manipulated to reflect the bias of those conducting the studies.
* It is better to have a loving mother and a loving father than to have two loving mothers or two loving fathers. "Never let that argument go," Prager urges.
* Avoid using the term "gay marriage." Use the phrase "same-sex marriage" instead. Under current law, gays already have the civil right to marry, just like anyone else. The issue at hand is whether a person can marry another of the same sex.
* If you dislike or hate gays, do not join the battle for traditional marriage. Anti-gay attitudes and behavior only provide ammunition for the media to portray conservatives as "bigots."
* Homosexual acts are a sin, but that is irrelevant when making the argument to people who don't care about the Bible as their source of ethics, Prager asserts.
* If it is argued that love should be the criterion for marriage, then raise such questions as "If two brothers love each other, why shouldn't they be allowed to marry?" or "If two men and a woman all love each other, why shouldn't they be allowed to marry?" or "If a father and son love each other, why shouldn't they be allowed to marry?" According to Prager, proponents of same-sex marriage will lose this argument in the public square because "Love is not the criterion for marriage. Man and woman is the criterion."
* Someone may argue, "If you're so concerned about protecting marriage, why don't you push for the passage of laws against divorce?" What does heterosexual divorce have to do with same-sex marriage? Yes, marriages fail, and divorce is tragic. Cars also crash and injure and kill people. This doesn't mean we should stop driving, though.
I don't see anything there addressing the claim that same-sex "marriage" will destroy the institution of marriage.
Excellent post, thanks!