Monogamy is one of the foundations that civilization is built on. It is so important not only in regard to making a stable environment for children, but for maintaining peaceful relationships between and within the sexes. That doesn’t mean that everyone has to be monogamous, we have always had exceptions, but as those exceptions become more common then civilization starts to break down.
We are having that now. We don’t practice old time polygyny, but modern promiscuity is a kind of serial polygyny where some guys, the “alphas” or “chads”, get most of the women while other less attractive guys get little female attention.
This problem is massively exacerbated by the welfare state and numerous laws which encourage female misbehavior. If, for example, we had a libertarian society, women who get pregnant from scum bags would have no recourse when that guy walks out on them and leaves them with a baby they can’t take care of. But now that we have welfare and forced child support, the state mitigates the negative consequences of women succumbing to the worst aspects of their nature.
On some basic animal level, humans want polygyny, like so many other mammals practice. Women want the alpha’s babies and men want a harem. The problem is that the “alphas” aren’t always the best guys. Sometimes they are just useless wastes of organic material who for some inexplicable reason can turn on girls. Like human peacocks. If those guys are going to have harems, both them and their concubines are going to need the financial support of “beta” males who are often way higher in quality even if they don’t have the same mating display as the peacocks.
With left wingers casting out all the old social values which have allowed civilization to exist for thousands of years, modern people are forced to reinvent the wheel as they learn that those values actually existed for a reason.
Free love is a myth, a liberal fantasy. Marriage exists for a reason. Jealousy exists for a reason. Gender roles exist for a reason. Pretending that free love can exist just leads to exploitation.
We would probably be better off with formally recognized polygynous marriage, like Muslims or fundamentalist Mormons, than we would with casting away marital fidelity entirely which is the current trend. Then the situation is entered into honestly and with greater stability rather.