'There's No Secular Argument Against Adult Incest'

Of course there is.
Extreme lunatic fringe religio-wingnut fascist Dennis Prager continued to promote the erroneous notion that a person can't be a good jew or "christian" and be a leftist at the same time because of incest.
Prager, like many religio-wingnut fascists, throws all kinds of shit against the wall in hopes it will stick. 
'There's No Secular Argument Against Adult Incest'

There are several reasons in reality - which we all know these perverts can't deal with - most based in Science - something these perverts really cannot comprehend.