Honestly, what personally bugs me is when one person has clear power over another. Parents and children for instance (especially when they are still children and unable to consent). At that point it seems less a relationship and more a case of one person forcing another. Ultimately, from a moral standpoint, I would have no problem with siblings being in a relationship for instance. I think the genetic aspect is blown out of the water and used as an excuse, as people aren't fine with sterile or same-sex incest either.
But I wasn't trying to move the subject to whether people are okay with incest or not. I realise it's a very strong and difficult subject, probably because the first thing peopel think of usually involves children and manipulation. Then again, people have gut feelings about polyamory for similar reasons (forced marriages of young girls) so I think it's important to go past gut feelings.
I think the main issue the general public has with polyamory or polygamy is their wrong perception of it. So I agree that any exposure can be good, for two reasons:
- It makes it seem less rare, unique, and as a result less of a thing only crazy weirdos do
- Any exposure to consensual multi-partnered relationship lets people know that it exists, and more exposure can show that not only it exists but it's the majority of cases.
The more that can be shown, the more people can realise that being against polyamory because they are against forced marriage of children is like being against marriage in general for the same reason.