A professor wrote Matt and expressed that he is in an open marriage because monogamy is unnatural. He said things like:
The truth that either escapes you or frightens you too much to acknowledge is that the “monogamous heterosexual relationship” is a largely unattainable (and undesirable) myth. Sexual unions between humans are not meant to be permanent. As we evolve, so does our understanding of these truths. Monogamy is not simply unrealistic; it is unnatural. You do not find it often in the animal kingdom, and where you do it is generally born of an evolutionary necessity. The necessity of monogamy among humankind has evaporated. This is particularly true of men, who are simply not biologically fitted for the “one woman” life.
You could use your platform for good but instead you use it to make those in open and poly relationships feel subhuman. Beyond the latent racism and sexism in your writings, it is your constant reinforcement of archaic relationship models that really does the profoundest of damage. Before you jump to any conclusions allow me to tell you this: I am married. I’ve been married for 15 years and my wife and I both sleep with other people. We are honest about this, which makes our open relationship more healthy than “monogamous” relationships built on lies.
Judge my choices if you like, but when you inevitably cheat on your wife, and then continue to sermonize about the sacredness of monogamous unions, I will return the favor.
Matt’s response is outstanding and worth the read. I would Love to know what the professor did when he read it. I do not understand “open marriage”. The whole idea… no the whole point of marriage is one man and one woman becoming one for life… it is very simple. Here is part of Matt’s reply: 
You say that men are especially ill-suited for monogamy. We are not “biologically fitted” for it. What does that mean, Professor? Do you go about your day and, before deciding on any particular course of action, ask yourself if it is something you are “biologically fitted” to do? I would say we are biologically fitted to be rational beings. And, as rational beings, we are capable of attaining higher things. Monogamy and loyalty are higher things. But are they more difficult for men? I can’t fathom why that should be the case.
I have found a woman who will be with me until I die, even while my hair falls out and my skin shrivels and wrinkles, even when I stumble, even when I fail, even through the doldrums of daily existence, through bills and dirty diapers, through all things — joyous or miserable, pleasing or painful — through every day until death comes. Why should it be hard for me to simply refrain from tossing such a gift into the garbage?
It’s hard for men to be monogamous? What a cowardly, pitiful statement. Also, how incredibly obtuse. It ought to be easy for us. Especially for us.
If you won 600 million dollars in the lottery, would you go out the next day and break into cars to steal the change from the cup holders? That’s what sleeping around is like when you’ve already found a woman who will pledge her life and her entire being to you for the remainder of her existence.