Open relationships are for psychologically weak, pussy whipped men. I agree they're a step up from the sexually frustrated truly monogamous man, who lives in complete self denial. An open relationship, though, just swaps in another sort of self denial. They're kind of like men who get off on being submissives, beaten with whips and chains and so on, men who enjoy being pissed on, men who enjoy being humiliated by watch another man fuck his wife. It's that sort of self denial, open relationship. While I'm all for a society that tolerates, perhaps even celebrates all kinds of people, that's not for me.
I recognize and act on the desire that we all have as men to be sexually dominant in a relationship, which means not letting our women fuck around. Men in open relationships sublimate that desire and perhaps get some sort of fetish like pleasure out of doing so, and for that I applaud them as superior to the man in a monogamous relationship. But they're still not fully actualizing their complete range of sexual desire.
The open relationship is just the latest form of Victorian thinking. It attempts to apply logic to the problem of sexual infidelity. The idea is that since it's obvious that we all cheat, we should embrace that cheating by allowing it for everyone, equally. That's nice. The Victorians were sometimes enlightened--that's why we called it "the enlightenment", and applied logic and reason to many things.
But it is at direct odds with human nature, and it is another form of self denial. Logic and reason can't be used to box in sexual relationships. It doesn't work. Not if you want to be a fully actualized human being.