Not sure exactly what the other fellow is talking about, but science is definitely relevant here. If you read the recent decision in the Michigan Marriage Amendment case:
http://www.freep.com/assets/freep/pdf/C4220110321.PDF
The basic question was: is there a rational basis to deny gay couples the same right straight couples have? One of the offered reasons for preventing gay marriage is that it was worse for children. That being a factual question, social science research was relevant. The short version: the judge, like other judges, found that the evidence offered favored the "gay people are just fine" side of things.