24. The stupidest argument or comment you’ve heard about non-monogamy, either for or against?

How about both?

For: That it is so-called natural (and monogamy isn’t), so everyone should be doing it (and not monogamy).
Any argument that contains the idea that everyone should be doing something is bullshit by me. I don’t necessarily disagree with the first part – it, like monogamy, is something that can be found in nature – so it is, therefore, natural. Heck, it seems to be the dominant relationship structure in some of our closest primate relatives, with whom we share a lot of our DNA.
However, we have social structures that are beyond what our DNA could have predicted. Monoamory works for some people, like my parents, so good on them. I’m happy for all of them. As long as they choose that without societal pressure (distinct from influence) and are aware of other options, should it start to not feel right to them, then I have no beef with that. I do have a beef against the idea that, because a lot of people are monogamous/monoamorous, that everyone should be, but that’s just the other side of the coin.

Against: Oh, there are far too many for me to pick the stupidest. Maybe “God made us to pair up into twos”?
Well, any religious argument is going to rate pretty high on the stupid for me. Why do you want me to be unhappy? Organized religion has never made me happy (at most, neutral) and I am pretty sure that I don’t believe in your god, nor am I sure that any such being exists (leaning towards no, but there are still some unanswered questions for me). So why do I need to follow your religious beliefs about relationships when I don’t follow your religion.
I’m not even going to take on how many non-monogamous relationships are portrayed in the Bible, because basically all of the male figureheads of the Abrahamic religions had more than one wife, and many had concubines as well. Heck, one could argue that the Bible is definitely in favor of non-mongamy, at least a very limited portrayal of it.