Barry Smiler wrote a great article There's No Such Thing As Polyamory and in my view spot on. We are moving to more personal freedom and responsibility. As Barry says:

The basic idea is that polyamory can be seen as simply a
subset or special case of everyone's right to self-determination in
all aspects of their lives. That is, polyamory could be reframed as
simply self-determination when applied to one's relationship life.

And If you haven't read Pete McWilliams book "Aint nobodies business but yours" it gives great arguments for ending Consensual Crimes including current sex crimes such as the law in some states against oral sex (free to read online or you can buy print copy at Amazon)

    This book is about a single idea—consenting adults should not be put in jail unless they physically harm the person or property of a nonconsenting other.

Chapter on relationships and the law is

    As of early 1996, adultery (sex with someone who is married, or sex with anyone other than your spouse if you are married) is illegal in twenty-seven states. Oral sex (called sodomy in some states)—either giving or receiving—is illegal for consenting heterosexual adults in fourteen states. Even missionary style, conventional, heterosexual sex between unmarried consenting adults is illegal in nine states. Cohabitation (living as married with someone you're not married to) is illegal in ten states.

    And let's not forget local ordinances. There are any number of laws—such as this one from Long Beach, California—which sound more like a passage from a Sidney Sheldon novel than a legal statute:

            No person shall indulge in caresses, hugging, fondling, embracing, spooning, kissing, or wrestling with any person or persons of the opposite sex . . . and no person shall sit or lie with his or her head, or any other portion of his or her person, upon any portion of a person or persons, upon or near any of the said public places in the city of Long Beach.

If business law had an equivalent to the laws concerning personal relationships, it would say, "If you're in business, you must have one partner, and only one partner, and keep that partner, until one of you dies." If this were the law, can you imagine the state of business in America? The same is true of the state of personal relationships.