Argument: Incest is actually not universally abhorred
"Sexual Ethics: Consensual Incest". A Nadder. October 13th, 2008- "It's universally condemned -- this was also used against interracial marriage etc. Again: so what? And again: no it isn't. It's universal to have some kind of incest taboo, but the limits vary a lot. In many cultures it's common for first cousins to marry (with up to 50% of marriages being between first cousins)."