I'm exactly of a mind with you. If it were handled well, my irritation would be minimal, and if it were done well ENOUGH I'd like it either way, but either because most people have so little notion of how open relationships could work or because they don't care (since the wives/gfs are still just an obstruction to them, however they decided to get rid of them), those almost never turn out well! I can't see at all how a story where they just happen to carry on an affair with someone other than their life-partners is preferable to an au. Even if that's an open relationship, it just seems bizarre and pointless if the third person doesn't have some significant characterisation as well. You can't devote pages to the one dude's mouth and eyes and poetically sexy posture and the heart-warming and affirming nature of having sex with him, and then 3-15 lines of dialogue to the supposed life partner. I've never seen any merit to the argument that alternate universes without SOs are inherently misogynistic. They're homosocial, yes, but that doesn't imply misogyny. Now, if there are no female characters in existence at all, and the story has much scope, you might have a point...