So having sex with your sister, a male and female relationship between two consenting adults is vile, but dipping your penis in feces is just fine.
If either is fine , incest is the more natural act.
Like poster number 2 says there is nothing evolutionary about homosexuality. No woman ever got pregnant from spit.,and the male does not have a womb .
I think the author isn't a nail-in-poo type, her construction is more tongue-in-groove...
The moral compass has one true north. Homosexuality might be the southern direction, while incest is another direction other than true. Both homosexuality and incest are premised upon lust, but not upon love.