I don’t like the idea of polyamory. It feels wrong to me. But when it’s consenting adults (or parties of mutual age in teens), there’s no argument against it.
That’s a big problem with people: not being able to reconcile their feelings with rationality. My feelings are irrelevant to how other people conduct their lives when it doesn’t affect anyone else. I think that’s a key component in having an open mind: to challenge your own feelings, to say, “I don’t like it, and that feeling is objectively wrong. I need to actively check my behavior so I don’t impose that feeling on others.”
It’s fine to have those feelings and good to acknowledge them, but you still have to think it all the way through.
Ah, the American healthcare system!