I’m very much for the idea that if you are not causing harm to others, and it’s just something you choose to do with another consenting adult, go for it. However, that is not true for incest where a child can be produced, as there is demonstrable evidence that it will harm the child and any of that child’s children. So if there is no possibility of a child being produced then I honestly don’t give a shit what messy bits get shoved into each other in someone else’s house.