The very first thing they established about the Starks & justice, was Ned telling his son the rule about performing your own executions. Then last season we had Sansa feeding Ramsey to his dogs, and now this nonsense, along with her explicitly calling Arya her executioner.

The really frustrating thing is how the TV audience is all about that whole "Stupid Starks" meme, and they pandered to it by making a big deal about Jon's impolitic declaration, when in the books, it was definitely portrayed between the lines how the Starks' ways, whatever the short-term weaknesses that might be apparent (and I have written at length elsewhere that Ned & Robb didn't fall due to their honor being a weakness, but by deviating from the course of honor), are serving them in the long run, as we are discovering a powerful attachment to the Starks among the northmen and willingness to go the extra mile for them, as well as the deterioration of the positions of the people who took shortcuts and pragmatically ditched the codes of honor whenever convenient.