@Killjoy - What time in our past do you mean? I'm afraid i dont know enough about that instance to comment on it but i'll look it up.
But i don't think that characteristic racial differences occurred due to inbreeding - i think that it was a gradual environmental effect on the peoples living in various ecological niches. For example more black people are taller an thinner than northern europeans - this is to do with surface area and body heat (Small, stout people lose body heat at a slower rate and vice versa for tall, thin people.)
@Spider - Incest may not lead to reproduction but the entire act is one of a reproductive nature. Thats why the act exists, why it feels good and why it dominates most of our concious and unconcious thoughts throughout any given day. I thought it was not unreasonable to equate the two. But when you look at someone you want to have sex with its most likely because messages are being sent to your brain and body along the lines of "that person would make a good other half to help produce my progeny".
That is not always the case of course, as we are capable of out-thinking our bodies sometimes but when you get down to it we are still very much animals and those reproductive signals are the same in humans and other mammals alike.
I dont agree with "You might as well argue that people with genetic defects should also not have sex. " People can have sex with whomever they want as long as its consensual, i am a great proponent of personal freedom etc. and would never stand in the way of something like that. Whether people with genetic defects should have CHILDREN is a different matter.
I can see what you mean but i am thinking more about the reasons behind the act and the possible consequences of such an act as opposed to the act itself. The act itself, in isolation, without consequence or a reason behind it that contradicts reproductive fitness, i guess would not be "wrong" but that situation can not exist.