Actually, biology doesn't support your argument; worse yet, the argument is flawed because it proceeds from the notion that evolution is a progressive path to an idealized perfection.
Unless I've been sadly mistaken (and misled) for the last few years...
Breeding sister to brother, whether its people or cattle or little fuzzy gerbils, is not a good idea over many generations.
My point was that incest (when practiced over multiple generations) can lead to some major problems in isolated populations.
The cheeta is a very good example of this in nature. Very narrow gene lines and slowly declining population.