They are opposing "Natural Law". Natural Law was what guided most of Founding Fathers in the development of the Constitution and even more so the Declaration of Independence. Natural Law is not some mystical concept, but the conscience of humankind. When you are following your conscience to are adhering to Natural Law. We all inherently know, even if we do not want to admit it, what is right and wrong. Homosexuality is wrong, the same way that bestiality or pedophilia are wrong. They are obvious deviations from Natural Law. No matter how hard the G&L crowd yells , Natural Law will not and can not be changed.
The natural law will order us dead. Simple.