Do kids raised by same-sex couples turn out as well as those raised by parents of the opposite sex? In recent years, the accepted answer among social scientists has been that there is no difference: Families headed by a mother and father are no better at child-rearing than those headed by two mothers or two fathers. “Not a single study,” the American Psychological Association categorically declared in a 2005 brief, “has found children of lesbian or gay parents to be disadvantaged in any significant respect relative to children of heterosexual parents.”

But was that conclusion – which has been cited many times – warranted? Loren Marks, a scholar at Louisiana State University, recently went back and reviewed the 59 studies on which the APA had relied. None of them, he writes in the July issue of the academic journal Social Science Research, “compares a large, random, representative sample of lesbian or gay parents and their children with a large, random, representative sample of married parents and their children.” Most of the studies were built on small samples that were neither random nor representative. In the absence of high-quality data, the “strong, generalized assertions … made by the APA brief were not empirically warranted.”

Assuming Marks is right about the weakness of the findings on which the APA’s verdict was based, how many advocates of same-sex marriage or adoption by gay and lesbian parents will consider changing their view? How many would back away from their support for gay marriage in the light of anything social science might say? I’d estimate the number at, roughly, zero. Conversely, suppose Marks’s paper had demonstrated that the APA’s declaration was even more firmly supported than previously realized. How many principled opponents of gay marriage would change their minds? My estimate would stay at zero.

In the same issue of Social Science Research, University of Texas sociologist Mark Regnerus publishes the results of a large national study, based on interviews with a random sample of 15,000 young adults (aged 18 to 39) about their families, upbringing, and life experiences. Regnerus’s bottom line: Children raised by their biological mother and father in stable families tended to turn out better than those whose parents had been in same-sex relationships. Even after controlling for age, race, gender, as well as subjective factors, such as being bullied as a youth, the findings were stark. Children raised by one or more gay parents, Regnerus wrote in an essay on Slate, “were more apt to report being unemployed, less healthy, more depressed.” They were also more likely to have experienced infidelity, trouble with the law, and sexual victimization.

Regnerus’s methodology has been sharply disparaged. Even some scholars who oppose same-sex marriage have underscored its weaknesses. Regnerus himself acknowledges that outcomes might be very different for kids being raised by same-sex parents today, “in an era that is more accepting and supportive of gay and lesbian couples.” And he stresses that sexual orientation has “nothing to do with the ability to be a good, effective parent.”

But even if his methodology were unassailable, would it change the larger debate over homosexuality and same-sex marriage? If you believe legalizing gay marriage is a matter of fundamental fairness, no scholarly study is likely to turn you around. And if you regard same-sex marriage as inherently immoral or absurd, a shelf of scientific journals touting its benefits won’t convince you otherwise.

We like to think of ourselves as rational creatures with a healthy respect for facts and logic and science. And yet when it comes to the most controversial questions of public policy – gun ownership, abortion, church-state separation, waterboarding, illegal immigration, you name it – does anybody start with the data and only then decide where to stand? Most of us move in the other direction.

Example: In a 2008 debate, ABC’s Charles Gibson asked Barack Obama why he wanted to raise capital-gains taxes, given that higher rates typically lead to lower revenue. “Well, Charlie,” Obama answered, “what I’ve said is that I would look at raising the capital-gains tax for purposes of fairness.” To Obama, raising tax rates on the wealthy was a moral imperative (“fairness”); revenue statistics were secondary.

Another example: Death-penalty proponents and opponents frequently wrangle over the deterrent effect of executing murderers. Yet even if the issue of deterrence could be definitively settled, advocates on both sides agree the debate over capital punishment would go on, as passionate and polarizing as ever.

Science and research matter, of course. But when minds change on fraught public controversies, it is generally in response to personal circumstances or an emotional appeal or societal pressure. Peer-reviewed scholarship, no matter how impressive, rarely has the power to shift us.

(Jeff Jacoby is a columnist for The Boston Globe. His website is www.JeffJacoby.com).