Barbara Currano states in her anti-gay-marriage letter that "the purpose of marriage is the creation and nurturing of new human life," that children of gay parents have a biological parent who is "deliberately disconnected from the child for the benefit of the adults," and that gay parents "cannot make up for the father or mother missing from the child's life."
Do I take it, then, that Ms. Currano is equally passionately opposed to marriage by heterosexual infertile or postmenopausal individuals, divorce, stepparents, and adoption? Because those relationships have exactly the same "problems" that she claims are reasons to ban gay marriage.
Ms. Currano cites research by Mark Regnerus purporting to show that adult children of gay parents have poorer outcomes than those of heterosexual parents. This particular study is deeply flawed: it was funded by the anti-gay Witherspoon Institute; and more importantly, most of the children studied were born to "opposite-sex" parents who later split up.
These children were all born during a period when gay marriage was illegal throughout the U.S. That is, NONE of these children are "children of gay marriage" in the sense that Ms. Currano implies, because their gay parents were ostracized and not permitted to marry. Most of them were closeted, trying to live a heterosexual lifestyle that wasn't their natural orientation, and one would expect that the breakups were not very pleasant. The negative outcomes seen in this study are therefore not a function of gay parents: they are a function of broken homes and instability, and their outcomes are very similar to those of children of unhappy, divorced parents.
Of course, living a lie isn't good for one's psychological health, and it isn't good for one's children's psychological health. When you think about it, this study is a case for gay marriage, because married gay couples have more stability than unmarried gay couples (and far more stability than closeted gay people trying to make themselves happy in a heterosexual marriage).
Same-sex marriage is not "experimentation" any more than life is experimentation. None of us know with certainty how our marriages will turn out: whether we will stay in loving, committed relationships that last a lifetime; whether we will have children; or whether those children will grow up to be happy, stable adults. But there is no evidence whatsoever that these outcomes are a function of the gender of one's parents.