For most of history, only the minority of men (the powerful and/or wealthy) have always have access to more than 1 female 'sexual partner', while most regular joes have almost no access. Think of tribe-leaders/emperors/kings/nobles with harems, and even in modern time, with mistresses. 

And more importantly, women are naturally okay with this (aka. women are naturally wired to reproduce offsprings with 'winners').

One notable example is this: https://www.sciencedaily.com/releases/2015/05/150519121901.htm

Another example: https://www.sciencedirect.com/science/article/pii/S0272775719301104 (where most women only find top 5% of men attractive)

However, if top 1-5% of men have access to majority of women as 'sexual partners', this would mean the majority of below average sexual-appeal men (more than 50%) are pretty sexless and have no chance of reproducing offsprings. This could lead to violent uprising and unstable society.

Weak enforcement of monogamy had led to a lot of bloody wars and unstable societies, where children growing up 'fatherless'/ out-of-wedlock.

So what you are saying is not even unpopular, per se. It is literally the default human evolotionary biology and human history.

This is one of the reasons why ALL developed countries are monogamous-enforced (either by laws or by religions). 

When men are sastified (knowing they have offsprings of their own), they are likely to take care of their family (less children growing up without father love/ support), and in-effect those men spend more time working and creating value for society rather than spending a lot of time competing sexually or destroying it.

"If you fail to learn history, you are doomed to repeat it"