Here's one of the most recent comprehensive studies done on the effects of the gay parenting on children: How Does the Sexual Orientation of Parents Matter? Judith Stacey; Timothy J. Biblarz American Sociological Review, Vol. 66, No. 22 (Apr., 2001), 159-183 Those of you who can't get access to the article itself (it could be tricky. I got it from JSTOR;) can check out this very elaborate reflection on it, or search the topic words on the USC main page, it should come up.
These guys reviewed 21 studies made during 1981-1998, and came to the conclusions presented below. They are supporters of the viability of gay parenting, which makes their criticism of past research most trustworthy:
p.176 "The findings summarized ... show that "no differences" claim does receive strong empirical support in crucial domains. Lesbigay parents and their children in these studies display no differences from heterosexual counterparts in psychological well-being or cognitive functioning."
Here's what they found:
p.167 "... our careful scrutiny of the findings they report ["no difference" mantra - Mel] suggests that on some dimensions - particularly those related to gender and sexuality - the sexual orientation of these parents matters somewhat more for their children than the researchers claimed."
p.170 "A significantly greater proportion of young adult children raised by lesbian mothers ... reported having had a homoerotic relationship ... The young adults reared by lesbian mothers were also significantly more likely to report having thought they might experience homoerotic attraction or relationship."
p.171 "Relative to their counterparts with heterosexual parents, the adolescent and young adult girls raised by lesbian mothers appear to have been more sexually adventurous and less chaste, whereas the sons of lesbians evince the opposite pattern - somewhat less sexually adventurous and more chaste ..."
p.176 "Evidence in these and the few other studies that focus on these variables does not support the "no differences" claim. Children with lesbigay parents appear less traditionally gender-typed and more likely to be open to homoerotic relationships. In addition, evidence suggests that parental gender and sexual identities interact to create distinctive family processes whose consequences for children have yet to be studied."
OK, so after 25 or so years of research the scientists arrived to the conclusion which Melikamp the Clueless intuited without any formal knowledge of the subject matter: the children raised by gay parents differ in a variety of ways, related to their sexual behavior and sexual orientation. While they cannot be classified as mentally ill in any way, they exhibit greater tendency for homosexuality. Their gender identity, as well, is affected.
Gasp! Who would think that the sexual orientation of the parent can affect the development of the child? We never saw this one coming.
With these results in mind, the proponents of the gay marriage still want to go ahead and place incentives on the same sex nuc'ular family structure, and encourage homosexual couples to raise kids who certainly will be different in a number of ways from the kids of the heterosexual parents. They, in effect, want to conduct an experiment on the scale of the nation, and use all of us as lab mice.
Even if we have no reason to be afraid of gays cohabiting and raising kids, I think it would be random and just plain irresponsible to give them marriage in its present shape, with all the benefits it entails.
Let me now exhibit what I think is the most obvious benefit: the tax cuts. According to a 2001 article composed by people at glad.org, "at the federal level alone, there are 57 provisions of the federal income tax code which distinguish between people based on marital status". These provisions serve no other purpose than to promote the marriage. There's difference between incentives like these and, for example, the laws relating to the acquisition, ownership or transfer of property. The latter ones serve to ensure that couples who expressed commitment and dedication to each other in marriage are treated as a single economic unit. In contrast, the tax cuts make it a desirable economic unit. I do not see any reason to make gay marriage more desirable than it already is. On the other hand, the heterosexual marriage was always seen as desirable and something to be encouraged, and that is especially because it has the procreative function, which same sex marriage lacks. I think that there are reasons to encourage the heterosexual marriage structure on the federal level, and these reasons are as old as the civilized society. May be we are at the stage where we need to evaluate them more carefully, because many heterosexual couples stay childless these days, and we are about to redefine what it means to "procreate". In any case, there are no reasons whatsoever to encourage the same sex marriage, because it already is beneficial to the spouses through its intrinsic properties.
I don't see any reason to withhold legal protections that make the couple a single unit. Inheritance, visiting rights, decision-making on behalf of the spouse all fall in this category. I think that we may have to recognise same sex marriage legally, but as a different kind of marriage; not because it's somehow worse than the traditional one, but because it is objectively (functionally) different. Giving them different legal names would be a good start. Radical left makes it look like gays have been struggling over a right to marry for millennia, whereas it's really been a few decades. This type of social structure is new, unparalleled in history, and there is no obvious reason to call it "marriage".
I would not be surprised if the transition happened naturally in the language, as the same sex unions become more common. What am I saying... Indeed, it already occurred, according to Webster; but that doesn't change the fact that the definition of marriage which US lawgivers were working with was, more or less, "the state of being united to a person of the opposite sex as husband or wife in a consensual and contractual relationship recognized by law". That, with a whole lot of talk about God, which the left tends to ignore as well. There's nothing in the Constitution about the same sex marriage; and saying that gays are treated unequally when they are denied "marriage" is a result of reading our modern biases into the text of the law.
To sum it up, "marriage" did not refer to same sex unions until very recent (personally, I'm not aware of any culture before 20th century in which it would be the case); Seeing that the family structures are functionally different, I think it is necessary to come up with new legislation, rather than misapply the old one.