Um, it's abusive in the fact that family members have a certain tradition of closeness and bond both physically and mentally that you can easily exploit. You're not giving your family members a proper experience in the dating scene. Biologically, two sets of genes mating that come from the same parents is beyond dangerous for offspring.
It makes perfect sense why human beings have evolved to show disgust towards incest. You're a creepy forget if you engage in it.
There are legal arguments against incest, just like there are legal arguments against loving dogs. But there are no moral or religious arguments for either one. It's still loving disgusting to forget dogs though
Wrong. Morality partially stems from evolution and biology. There are legitimate moral grievances to be had.