Thanks. Context is everything.
As concerns Indiana's law for first cousin marriage, I believe the reasoning was related to not only the prevention of the births of children with a higher likelihood of defects, but also the idea of upholding the image of the ideal family in the classical sense (married mom+dad+kids). Obviously 65 year old people cannot produce their own children. But equally important is that it is exceedingly unlikely that 65 year old couples would adopt. Society's notion of the "ideal family" was thus encouraged by the marital laws.
