What is wrong with polyfidelity? Nothing. Or everything. Anything that could be wrong with anything, or could not if you are doing more respectful and aware ways of relating.
What is WRONG with monogamy?
Not a damn thing necessarily. Plenty COULD be wrong...in particular relationships...
But I think they are focusing too much there on
a.) "Rules" being a mechanism forced upon one person to restrict their behavior, by another person who is being controlling, or possibly a couple towards a "third" or whatever.
b.) The common convention of the new couple that has just opened and is not comfortable straying TOO far from the safe structure of mono, so they're just doing monogamy with more than one.
Are those things, things that happen? Sure, ok. But are they always the case? No! That would be like saying that because my marriage was abusive, all men or all husbands or all marriage, or all committed relationships, or something like that, cause abuse by default and should be avoided. It just ain't so.
I could start a thread about how, since there could possibly be problems a, b, and c, about relationship anarchy, or solo poly, or whatever, titled "The problems I see with..." I could start one about all of the instances where dogs have bitten people, and title it, "The problems I see with dogs." The point might be kinda situationally valid, but holy sweeping judgmental generalizations, Batman!
How about, "Are ya happy? Are your partners happy?" If so, then you are doing it right. For you. Easy.