This is an interesting thread.
I think BS's want to believe that most of the people think like Aristotle or Plato or Kant. Who argued that the key element of ethical thinking is "character" (Aristotle and Plato) or "duty" (Kant). I think the reality is most people think like Machiavelli. Who argued that the key element of ethical thinking was the consequence of the action taken.
I think the vast majority of the people are Machiavellian, but appear to be "Aristotlean". This is because, in general, good consequences come from following one's duty (or laws) in accordance with one's virtues. But there are times when this does not hold true. Times when a person feels they must violate their sense of duty and virtue in order to achieve a good result. The man speeding through traffic, running red lights, to get his injured child to the hospital, has revealed himself to be Machiavellian.
I find it ironic that most people embrace a Machiavellian approach when they are on the good side of its consequences (the child or father in the example above), and despise it when they are on the short side (the guy who got run off the road) of its consequences. But I suppose it has to be that way, else we would have no "certainty" in our life. How could we function if at anytime we could be the victim of someone else's good consequences. So, we pretend that most embrace Aristotle's view and Kant's view. Then when we are the victim of a Machiavellian assualt, we debate the flaws of that individual, so we can once again feel safe. Then we reveal our Machiavellian side saying, it doesn't matter about my moral view on marriage or divorce, doesn't matter what "duty" was created by my vow, if circumstances don't change, I will choose a course of action that leads to a "good" result.
Harley says there is no such thing as unconditional love. I think that is true because their are no Aristotle's or Plato's or Kant's. (I seriously doubt they actually "lived" what they "believed"). Just a bunch of Machiavelli's. BS's and WS's both.
Because of that, I don't think the BS has the moral "high ground." What they have is the judgement "high ground." If one truly believes that they are unloved by their spouse, love and are loved by another, divorce will crush their spouse, they are trapped in a life of suffering, nobody will ever find out, and everyone will be better off, then the majority of fault lies not with the action they took, but with the assessment of their situation. For me, the questions that roll around in my mind are not how could you do this, but how could you think I did not love you? How could you think you loved someone else? How could you think they loved you? How could you think divorce would destroy me? How could think you are trapped or suffering? How could you think I would never find out? How could you think we would be better off? It's poor judgement.
And good judgement is what shields the BS, who's gone for years with out having their EN's met, from an affair. Put them in the exact same situation as their WS, and they will not draw the same conclusions.
If one wants to argue poor judgement is a character flaw, then so be it. But then good luck finding a person with flawless character, because I've known no one who hasn't suffered a case of poor judgement.