My take: Incest is shortsighted. It's ignorant. The biological reasons for not doing it even when using contraceptions run to psychological and spiritual misconceptions. It is unhealthful. It is the opposite of wholesomeness.
The more intelligent (some say evolved), the more genetics insists that mating be less and less incestuous (think deformities, etc.). The human brain is not disconnected from this even where condoms, etc., are used. A condom on the penis, for instance, will not protect the brain from the damage. It will not protect society at-large from the damage.
Excess and license leads to more of the same in other areas. Error begets error. Depravity begets depravity. Sexual error is not completely separable from violence and greed and other forms of selfishness/shortsightedness.
The arguments for incest are based upon disjointed reasoning, fractured thinking.
Michael Brown begins his article with the following:
If all human beings should have the right to marry (or simply be with) the one they love, as proponents of same-sex marriage constantly tell us, then why shouldn't adult, incestuous couples enjoy that same "right"? Hollywood director Nick Cassavetes is the latest to say, "Why not?", and I for one am not in the least bit surprised.
Read the whole article (recommended!): Here Comes Incest, Just as Predicted - Michael Brown