It appears that I have been misinterpreted--in exactly the same direction as professional psychology's beliefs about monogamy. My intention was to note that: 1) Professional psychology ASSUMES that long-term monogamy is the "healthiest" sexual arrangement; 2) There is little evidence that this is actually the case; 3) There are important clinical and political implications for this assumption.
A key aspect of therapy is helping clients see their own invisible assumptions--about themselves, the world, "men," "women," "sex," "love," etc. Similarly, psychologists should be equally devoted to recognizing our OWN assumptions, challenging beliefs that have no basis in empirical data. For example, professional psychology assumed, for decades, that homosexuality was a mental disorder--using "common sense" (or, more likely, a combination of ignorance and personal discomfort) rather than actual data. When Evelyn Hooker administered MMPIs to gay and straight people, professional reviewers could not distinguish the unidentified test results of gay people from those of straight people. Now that's data, and it did indeed eventually help eliminate "homosexuality" as a pathology from subsequent DSM editions.
So what data does our field have for its beliefs about the superiority of long-term monogamy? Remember, it's particularly unusual among American adults. And if we simply use longevity of marriage as the basic measure of emotional or relationship health, we are obviously missing the boat. The fact that most people who marry (which, remember, is not everyone, and certainly not everyone at age 21) pledge sexual exclusivity does not mean that this is their preference, or their actual intention. In any event, life-long sexual exclusivity is certainly not the norm in Western culture. If we say that "most people fail at it becuase they aren't grown up enough to make it work," that's simply a tautology.
In addition to examining our own bias toward this particular form of sexual relationship, I think we psychologists would be well-served if we asked ourselves how this assumption became so sacred to us, and how we managed to not notice this reification for so long.