I understand that our social 'norm' is monogomy.

I just distrust the forms of brainwashing (IMHO!) that lead people to believe that it is either 'normal' (aka 'natural') or indeed plausible, to lead their lives in such a fashion without encountering severe reality checking.

GMF is completely 'normative' within other cultures, as is arranged marriage, or indeed abduction and rape leading to marriage, but it doesn't necessarily make it the most constructive or enlightened approach to adopt in a self-professed "enlightened" society such as the West.

Strong examples, I understand. But agreements made under extreme social pressure, or before an individual has had enough personal experience to determine their own values outside of collectively assumed/indoctrinated ones, will mean all kinds of people get pulled into contracts that are not in any way right for them.

How do we feel about people that go AWOL when they disagree with a governments aggressive foreign policy, or Civil Servants who break confidentiality, in public interest for example. These people are breaking promises and contracts too.
Is it ever as black and white as that?

Think of the amount of Gay men, who have had families because homosexuality was not 'normative'? How many of those who broke their eternal promises, would we condemn as cads?