The bolded part is where we disagree. I don’t think it’s true. I agree that nothing’s been terribly effective thus far, but I think that’s because we’ve tried varying levels of oppression and repression thus far, and I think that’s the exact wrong way to go about it.
What no one’s tried on a large scale - or at least tried lately - is open and honest sexual relationships with more than one consenting adult. That’s a pretty new experiment (the open, honest and consenting parts, not the more than one part) and I don’t think it’s been going on long enough or widespread enough to declare it a success or a failure yet.
Before the torches are lit, let me say once again that this doesn’t mean I think everyone is polyamorous or that everyone should be polyamorous or that poly people are “more evolved” or anything silly like that. But I would like children to be taught that monogamy is ONE way, and if it works for them, great, but there’s another ethical way to conduct relationships as well.