Animation Source Forums

It's the fact that it's not appropriate for children...
hence why it's not mentioned in the movies and would probably mean not appropriate for this site either.

And from what I know of some breeders, incest among animals messes up their offspring down the line
and makes them more vulnerable to diseases and deformities... from what I've heard anyway... >.>

Thank you for posting this. Whether it's acceptable for a kids site or not, you put it in the words I couldn't put together. I full on support this answer to all of those questions. Thumbs up. It is, indeed, completely true.