People really blow the genetic mutation thing way out of proportion. Basically the biggest risk is that two related people would posses the same dormant genes. It's not like oh you're brother and sister, you're baby is just going to be retarded by default.

There's a famous example of one side affect of incest, the Hasburg family.

http://www.antiquesatoz.com/habsburg/habsburg-jaw.htm

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  Here force failed my high fantasy; but my
desire and will were moved already-like
a wheel revolving uniformly-by
  the love that moves the sun and the other stars.

However, from a biological standpoint, incest is quite wrong. In order to keep the gene pool varied, it is imperative that people from the same blood line don't reproduce. I'm not quite certain which state it is in, but the famed "blue people" from the Appalachian area bring up an excellent example of what inbreeding can do to people. Very similar to this is the family history of hemophilia in the Victorian royal family.

Basically, yes, I have a problem with incest, on not only a moral, but also a scientific level.

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a deafening silence
rings on in my heart.

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. I'm not quite certain which state it is in, but the famed "blue people" from the Appalachian area bring up an excellent example of what inbreeding can do to people.

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The disease is called methemoglobinemia.

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  Here force failed my high fantasy; but my
desire and will were moved already-like
a wheel revolving uniformly-by
  the love that moves the sun and the other stars.