While on the surface that may appear to be true, it is worth noting that people who undergo or move past the mental boundary of attempting incest are to a marked degree much more likely to have comorbid mental illnesses or disorders. Along with that, undergoing incest has been shown to cause a marked shift in the psychic of an individual, much the same way the human mind “breaks” when forced to undertake cannibalism. This change is not healthy, and despite it not always being visible, this change carries effects very similar to severe PTSD, even in seemingly loving and consensual relationships.

Evolution is extremely adamant that incest does not occur. To the point of breaking people that attempt it.

To me it’s not a moral disgust argument, but much more along the lines of someone wanting to shot themselves in the foot with a rifle. Because while yes, there is nothing stopping them and they consensually want it, and they aren’t harming anyone else; it becomes a case of “Wait! Stop that person, they’re about to make a huge mistake that’ll severely negatively affect them”.