This article could use some nice infographics and charts. The way it is written makes it hard to see exactly how things have changed over time.
https://en.wikipedia.org/wiki/Value_of_life#Life_Value_in_th...
(Of course, there are exceptions where people effectively pay rates of many billion dollars per life to avoid emotionally salient risks, like terrorism.)
The OP article gives the misleading impression that society's changing values are mostly due to moral progress (presumably arising, I guess, from people being persuaded by moral arguments, or from certain societal norms taking hold). But it's almost certainly the case that you can explain the vast majority of the change by economic developments, especially following the dramatic rise in per capita wealth starting with the industrial revolution. The dark implication of this is that if per capita wealth falls drastically in the future, which is possible depending on technological developments, then we are likely to see a regression in moral attitudes.
The way this happened in our history (I'm assuming that it's not the only way) is through institutions like The Old Bailey and the codification of laws and the visibility into the not always completely fair, but always getting fairer, application of those laws that they provided.
Medieval Iceland lived for 300 years without a government. Murder was punished by fine or exile, or becoming a slave or worse, an outlaw, if they refused to pay their debt to the victim's kin. This period is very well documented. Maybe you could find the exact value murderers were fined. That would give us a data point for 1000 years ago.
And at one point in ancient Rome theft carried more severe punishment than murder.
Germania was a poor province, when Rome tried taxing it, they got very little. Maybe it seemed wasteful to Germans to kill yet another man after losing one, when they could profit instead. To the Romans, prevention was the priority.
The same probably applies to the social norms. The brain of human beings could not change too much in such a short period of time. So, most likely we did not become intrisically better. Yes, the social norms were improved significantly, but mostly thanks to the improvement of the quality of life.
I think, it's all about utility. Killing a person does not necessarily makes the murderer richer, most likely not; on the other hand, stealing something actually makes the thief richer, so the law in the past had to take coutermeasures. Nowdays, police works better, it's likely that you will be caught if you steal something, so the utility of stealing is pretty low, and the risk is high. On the other hand, a murder is frequently not about money, but hatred and personal relationships, this motive is less rational, and the utility of a murder can be rather high, even if it's likely that you will be caught. Of course, I did not do any analysis..
And it is very pleasing for us to think that we are much better than we were in the past, and out moral standards are higher compared to the crazy stuff we did before. But this bragging is just a reiteration of the words of William Blackstone cited in the article. In fact, we are not better, we just live in different time, and it is rather stupid to assume that just a few centuries ago we were less rational and less optimal. Most likely, the old cruel law was great and optimal in that historical period.
Not to refute your point, but there is a further interesting dynamic described in the article: feedback. English legal practice is based on precedent in common law. There is a ratchet effect whereby past rulings influence: subsequent rulings; behaviour (morality) of citizens; perhaps too, laws subsequently enacted by those citizens' elected leaders.
I suspect the OP, who is connected to the Santa Fe institute, is interested in exploring such an emergent system.