There is nothing wrong with polyamory in theory. It will, however, in practice, fail 9/10. This is not because polyamory itself is wrong or degenerate, but because it requires an INSANE amount of confidence and maturity.
I may be mistaken, so take this with a grain of salt, but a good amount of people don't have the confidence, that is to say that they are not insecure, for monogamy, let alone relationships that involve more than one person.
I may again be mistaken, but I believe that most polyamorous relationships happen with teenagers and very young adults, people who often do not have the self-esteem and maturity to generate long-lasting monogamous relationships, let alone anything else, and then you have all those husbands and wives who are in bad place in their marriage, be it because they have fallen out of love and cannot get themselves to end it all and admit that it was a "waste" of their time or because it should never have gone that far in the first place, people who are most certainly not in the best mental shape when comes to matters of intricate intimate interpersonal relationships.
That is not to say that there aren't huge cunts who just want to get away with cheating, that is certainly true, but then again, those people would likely be giant assholes in any kind of relationship anyway. It is not the polyamory that makes them bad, they are just cunts anyway.