>>81548600 (OP)it's an unhealthy relationship dynamic. you're related, now you're going through the motions of either a partnership (not legal, not practical since offspring are ultimately the point), or you're becoming fwb (deeply complicates sexual development). now instead of having to develop normal tendencies and attitudes, it's like "oh well i can just shag my brother if im horny". it's not good. it also results in hard feelings when someone decides to go get into a real relationship with someone outside the family.
it's just a terrible idea. there is no benefit that cannot be gained from normal sexual activities yet carries a number of downsides. anyone unironically campaigning for incest is willfully ignorant of the cost-benefit simply to fulfill their fetish, which ironically enough, also likely stems from poor development and/or premature exposure to pornography