Yes. I think that's reasonable. Having sex affects only those 2 adults, but having children affects those children.
And why you always gotta call yourself Kadark the Something?
At least be honest and call yourself Kadark the Annoying.
So then, you support eugenics? If the man in a heterosexual couple, for example, has some sort of a disorder which can potentially be passed on to the child genetically, would you say that the man shouldn't be able to have a child with his wife? After all, it "affects the child", as you put it. But ... the only way to enforce this, like with incest, is to sterilize the man so he can not pass on this disorder. Pretty soon, you're sterilizing people who have disorders/some sort of genetic inferiority. Kind of reminds me of Nazi Germany. Sucks getting tangled in your own faulty logic, doesn't it?
Kadark the Principled