While I agree in principle I still feel there are situations where one side is so disrespectful and or destructive, that despite all vows they can no longer expect unbroken loyalty of their partner.

Don't get me wrong, two wrongs never make a right, but the reasons why people behave the way they do tell more about a person than their actual behavior. Cheating is never right, but sometimes what it tells you about the person is more them being a tragic person than a bad person. It depends.