Can it perhaps be time that we stop saying “ethical non-monogamy”?
Nobody feels the need to say “ethical monogamy”; monogamous folks are given the benefit of the doubt and assumed to be practicing a relationship ethically.
I feel like polyamory, open relationships, relationship anarchy and other forms of non-monogamy are now sufficiently accessible to popular culture that we can drop the word “ethical” and still be understood. (Ideally we do so before it starts to look like virtue-labelling.)
Or do it by exception – cheaters and such can start call themselves ‘non-ethical non-monogamists’.