I'm a firm supporter of the word polyamory. But that one is close to my heart.
I'm certainly not suggesting legalization of polyamory. But it's also unfairly judgmental of you to compare such relationships to the criminal acts of bestiality or child sexual abuse.
There will be other forms in addition to our classic marriage. One is already looming on the horizon: polyamory, or having more than one intimate partner.
I understand polyamory is different from polygamy, and doesn't share the latter's rigid and noxious views that men run the show and are the only ones allowed multiple partners.
Polygamy has an ancient history and is legal in many parts of the world. I find the rules of polygamy to be damaging and it's potentially dangerous to young girls and terrible for "excess" boys. But polyamory is supposed to be a more equal arrangement among agreeing adults.