If you feel the need for an extra partner, you didn’t choose the right one in the first place or aren’t putting in the effort to make it work.
Personally, if I was with someone who even uttered the suggestion to me of being polygamous I’d leave them immediately on principle of essentially wanting to fuck other women? Actually, I can say this for certain, as I was faced with this after 10 years in a relationship and walked away. I’ve never regretted it and I am now with a man who is also monogamous. If they don’t want to be with me then they’re certainly not gonna have a help yourself, as you please, open buffet to me as well as any old random they meet. I know I’m not the only person that would be insulted if their partner wanted to do this.
I would love to say, each his own as long as everyone is consenting, but unfortunately, too many articles speaking positively about polygamy have a male-dominated presentation of polyamory. I have very rarely seen an article or defence of polygamy with a woman-led relationships. That’s what polygamous people should be shouting about, because it’s sexist bullshit and literally reinforces patriarchy. As long as society is okay with polygamy for men, but not for women, then it will always be an issue in my mind.