Comment #214685 by Cartomancer,

Not sure how relevant it is but I think some of this might be hardwired in a sense (by no means saying it's a good thing, in case that needed saying). I remember an hearing Steven Pinker talking about negotiating tactics that could be used with people that have some idea of your thoughts. It works out that in certain circumstances the less reasonable you are the better your outcome.

It may very well go a ways to explaining why people will brutally and descisively defend their honour. I imagine that this would provide an increadably strong impetis to take such peoples threats seriously and therefore provide an evolutionary advantage. Love's very nasty flip side I think might be murderous jealosy.

Mix this with an unhealthy dose of patriarchy and religious certainty, devalue women to just above cattle and it's not entirely unusual to see this sort of thing emerge.

I think our western values are harder won than some people think. People need the right environment to act well to one another, without it well...human nature has a nasty side.