If the Vikings saw that the possibility of revenge led to a risk of unending cycles of violence, and therefore implemented peaceful workarounds to avoid revenge, isn't that a good example of the possibility of revenge limiting violence? If there were little risk of revenge following a violent attack, that would plausibly make violence more likely. Trying to model this behavior would indeed be difficult and complicated and, perhaps, not as reliable as that presenter suggested. By the way, I look forward to another episode of Fooling Garwulf!
Well, not really, I'm afraid. What they did was implement a system of blood payments, aka Weregeld, and make certain acts legally free from retribution (human sacrifice and execution for a crime being the two main ones). So, the actual result was that on raids, people would be sacrificed to the gods to prevent retaliation (in short, subbing in a form of violence they could get away with), and in blood feuds, you'd see violence followed by lawsuits to de-legitimize it, followed by retaliation, followed by more lawsuits. Seriously, the feuding families in the Icelandic sagas seem to spend about as much time in court as they do killing each other. So, to be pithy, the amount of violence was about the same, but there were more lawyers involved. And, thank you! The next installment of Fooling Garwulf goes up tomorrow afternoon, assuming all goes well.