I like this question — I don’t think someone’s relationship choices make them inherently a good or bad person if they are up front and honest about their intentions.
To your point, if someone doesn’t want monogamy, and they openly and clearly express that to their partner(s), AND THE PARTNER(S) AGREE, then no harm, no foul.
As far as I’m concerned two consenting adults can go ahead and do whatever they want.
I wrote this article to focus on the problem that arises when someone says one thing, and does another.
So, that actually wouldn’t fit into the category you’re describing. I’m talking about dishonesty or misrepresentation of intentions — THAT is a problem.
However, being clear about what you want and then living in accordance with it, as long as it’s not hurting anyone, is always the right path.
My 2 cents.