Well there is that little thing about deformed children that you need to work out first.
So it is conditional. Lets rearrange your statement.
Well there is that little thing about deformed childrenAIDS that you need to work out first.
But homosexual sex between brothers or between sisters can't produce children, so that argument couldn't be used to outlow homosexual incest. But then if you legalize incest between same sex siblings, but leave it criminalized for heterosexual incest then that is discriminatory. And what about incest between brothers and sisters where one of them is sterile? You seem to be suggesting that the government should not have the power to pass legislation on this issue.
Actually, there are more recorded deformed and/or genetically disposed diseases ( hemophilia ) of the progeny of European royal cousins.