There's literally no reason to be against incest. I'm serious. Walk with me.
Why is it that people think it's wrong?
Because abuse can happen?
It can in any other relationship.
Sure, but you're worried about the abuse that can come from it, yeah? Refer back to the first point.
Because they might have a disabled child?
... You do realize that's quite literally eugenics, right?
Oh, you're worried about putting a person through unnecessary suffering by being disabled?
Oh okay, so you must also think disabled people shouldn't procreate either, right? Their children might catch some unsavory life. Eeew-
Oh wait, sorry, what was that?
You don't think disabled people should be barred from having children?
I'm sorry, but can you explain to me the difference between those two things then?
What if they can't procreate? What then?
There are abusers in all types of relationships.
Would I personally be suspicious of a child/parent incestuous relationship if I don't know them?
Would I make a snap judgement and take away their right to personal freedom under no other circumstances other then it's incest?
Would I personally protect a person from actual abuse if I saw it no matter the relationship?
But genuinely. There's no reason to be against it if you're a decent person. If you're worried about the abuse or grooming, be worried about the abuse and grooming!
Incest is not inherently abusive. It's not allowing for informed consent that is abusive.
Thanks for walking with me.