I think that "humans tend towards monogamy" and "humans don't tend towards monogamy" are both misleading, as they lump together two things which don't necessarily go together: being monogamous, and requiring monogamy of others. Instead, I'm inclined towards thinking that there's a tendency to require sexual/romantic monogamy from one's partner while still wanting to have sexual/romantic relationships with others.

Though some people seem to be strongly monogamous (in both senses of the word) by nature, others seem to be strongly non-monogamous (in both senses of the word), and some fall in between. So if there is a strong genetic component, there's also the possibility that some kind of frequency-dependent selection might be going on instead of just a universal tendency towards one thing.

Monogamous (for how long?) is probably a very important question in discussions of to what extent monogamy is natural for humans.

Is there a convenient term for raising that sort of question and/or filling in that sort of blank?

Yes, humans are bad at plenty of things they want (or seem to / claim to want). Bad at rational action, yet members at this site strive to do better. Bad at ethical & consequentialist reasoning, yet many of us strive to do better.

So being bad at monogomy is not a particular good argument for abandoning it. But maybe you didn't mean to imply that -- I speak to it because I've heard that claim from a few poly folks before. If so, disregard.

If you just meant to clarify that, yes, humans are not perfect monogomists, then okay, we're agreed on that.