I believe that my point has been missed. I did not intend to suggest that I necessarily agree with Dr. Millon on what pathology is and is not. Rather, I was pointing out that we do not have any one logically consistant organizing principle for the creation of a nosology of pathology (e.g., the DSM). We have resorted to political correctness, social pressures, and God knows what else, and them some science (a lot of it really bad science).
Thus, if we are going to sit in judgment about what is "healthy" (which is just another way of saying moral, really), then we need to be willing to examine our assumptions of what is "healthy." I certainly would agree with your point that the assumption that monogamy is "healthy" has its root in Judeo-Christian thought, but that does not make the assumption wrong (unfortunately, I must admit in a logical and scientific discussion that it does not make it right, either). I can also say that it is consistant with my experience as a clinician.
As for evolution... that is a set of assumptions and pseudoscience as well. But, I will not go into that tangent, but will refer interested readers to Phillip Johnson's _Darwin on Trial_. Dr. Johnson examines the evidence for evolution and argues that it is itself a religion (I know someone's neck hairs are standing up as they have read that ;-).
I'm not suggesting that assumptions are wrong or bad (we make them, and we can't help it), but we can be honest about it. Thus, my question is: what assumptions underlie the suggestion that perhaps open marriages are superior, or rather than monogamy is inferior? In addition to the assumptions, what evidence can be forwarded in support of such a position? How might a research study be carried out?