Talbot explains why both sides in the Prop 8 case have paid so much attention to whether sexual orientation is genetic and fixed:
One of the four criteria for defining a classification such as sexual orientation as suspect—which in turn subjects laws targeting that class of people to the highest burden of proof—is that the group in question share an immutable characteristic. The immutability of sexual orientation is hardly a settled matter—just ask Anne Heche. But maybe it needn’t be always immutable—just generally a matter of deep internal promptings that would take some serious suppressing to get over. The three categories that the courts have said in the past warrant strict scrutiny are: race, national origin, and religion. The first two are clearly immutable, in the sense that most people think of the word, but religion is not. Indeed, it might well be that people convert, are born again, or lose their religion altogether as often as they switch their sexual preference.
The Dish 