Unless you deliberately want to engage in advocacy to change society's view on a topic or persuade other people keep controversial opinions to yourself. If you aren't sure test the waters only in appropriate contexts without committing to the opinion which can let you safely gauge reactions.
I'm assuming these are mostly theoretical concerns not things you want to do yourself but without being judged.
FWIW I'm not the main character nor is anyone else.
FWIW #2: The sibling effect naturally causes partner aversion to any other children you spend a certain amount of time with growing up. Normally functioning brains exclude these people as romantic partners, though there are "exceptions" like siblings or cousins raised apart from each other. That's the source of the cultural taboo so you're gonna have a tough time getting anyone to sign on to that opinion. We evolved this way to prevent inbreeding so it's a fairly strongly preserved trait.