You are an idealist and an anarchist, probably living in wonderland, in your own little bubble that has nothing to do with reality. If most people were as enlightened as you think they are, there would be no need for the law indeed. Since they aren’t, we have the law. And based on the law, a neighbor can call the police or child services on you for living with multiple husbands. The next thing that would happen is kids taken away and mom locked up, very likely including her husbands. Especially in places such as Trump’s America, but elsewhere too.