Sadly no studies for correlation of attractiveness to instances of incest exist, which needs to done... But I have no arguments against incest from the studies that do exist. It takes 3 generation of continuous incest, with that being father and daughter, father and his new daughter, and even then father and his daughter. 3 generation of the same father fucking his daughter-grandaughter-greatgrandaughter, for the risks of incest related birth defects to reach about 30%. That level of continuous incest is incredibly unlikely to ever occur. With brother and sisters and their offspring fucking cousins and those offspring fucking father daughter and those offspring fucking brother and sister still only puts birth defects at 14-16% at the absolute highest... Lets put this into perspective, A woman at 27 has a 12-16% chance, at 30 has a 23% chance of producing a child with a birth defect, a woman at 40 has an 86% chance.
Incest over 20 to 30 generation could cause serious problems, but unless you live in them most isolated homestead possible, incest that carriers on for that many generations in quite impossible for anyone but royalty to achieve.
This just shows that the JBpill is the only pill that will save humanity. I don't think incest is wrong, but so many people do, and to those people who do think its wrong, women over 23 years old giving birth is already worse for the future offspring than a father fucking and impregnating his own biological daughter.