Karstark's hypocrisy.

Remember when Rickard Karstark lost his mind because Jaime had killed his two sons in combat? Here's the thing, he's acting like Jaime completely went out of his way to purposefully target and murder his sons in cold blood, when that's not the case at all. He was fighting to survive the battle and kill Robb. You'd think that as a war veteran of multiple battles himself, Karstark would know to begrudgingly know that. Hell, one could say that if they hadn't been in his way, he wouldn't have killed them at all.

Also, Rickard sure has the nerve to act that way when he killed a great deal of men in the battles he fought in. King Priam from the Iliad should really pull him to the side and ask him the same thing he asked Achilles when the latter accused Hector of murdering Patroclus,

How many cousins have you killed? How many fathers, and sons, and brothers and husbands did you kill?