Ultimately, I think that the most reasonable conclusion to draw with respect to moral luck is that it is a mistake. There can be no justification for intentionally doing harm to people – to saying that they deserve to be harmed, based on things that are outside of their control. People may (and do, in fact, on a daily basis) come to suffer harm as a result of things beyond their control, but those factors do not affect how much harm they deserve.
We have a natural desire to harm others according to the harm they have done with us. We are tempted to strike back more forcefully against those who inflict significant harm than those whose attempts at harm (or whose lack of care) happen to cause us no ill effects. However, if a mere desire to do harm were enough to justify the harm done, then no harms done are ever immoral. Every agent who intentionally does harm has some desire to fulfill in doing so.
We can guess as to where this desire comes from. Among primitive animals, who lack the capacity to theorize about underlying mental state, harm done is a reasonable approximation of harm intended. We need a rule of thumb that is simple enough for chimpanzees to understand. A rule that takes the measure of the desires that are thwarted and prepares a proportional response is such a rule. This also applies to the complimentary rule (no pun intended) that takes the measure of the desires fulfilled and prepares a proportional response there in term of gratitude and reward.
However, as our capacity to understand more complex relationships between desires, intentional actions, and the thwarting of other desires grow, we may discover that these primate and simplistic solutions are unjustified. Morality, after all, is not to be grounded on how we do feel about a particular set of actions and responses, but on how we should feel. The desires that linker from our more primitive states are not necessarily the same desires that more intelligent beings should encourage.
Still, there is something to be said for the primitive and simplistic rule that the harm done is a reasonable first approximation to harm intended. It is not unreasonable to at least begin with that assumption in most cases, and to deviate from that assumption only to the degree that there is reason to do so.
The typical person who assaults another does not intend to kill. If one person fails to kill another, there is reason to begin with the prima facie assumption that this individual intended only to assault and not to kill, so the conclusion that he lacks an aversion to killing is not justified. At the same time, if the victim is killed, we may begin with the assumption that the agent intended death. Using that as our starting point we will then require evidence that the death was truly an accidental result of something that should have turned out much less severe.
However, this is not moral luck in the sense that a person deserves to be harmed based on circumstances beyond his control. Rather, this is epistemic luck – the fact that luck has an influence on how much we know about an agent’s culpability.
We can be fully confident in the fact that there are some horrible people living comfortable lives free of any condemnation or punishment simply because we do not know the evil they do. And we can be equally confident that innocent people are, even today, suffering horrendous punishments up to and including death.
These are not cases of moral luck. The first of these examples deserves far worse than he is getting, while the second deserves far better. This is epistemic luck – the fact that our imperfect knowledge prohibits us from doing harm to all those who deserve it and saving from harm all of those who do not deserve it.
The assumption that those who do not kill do not intend to kill, and those who do kill intended it, represents this type of epistemic luck influencing actual praise, blame, reward, and punishment. It does not represent moral luck in the form of how much praise, blame, reward, and punishment is actually deserved due to circumstances outside of the agent’s control.
The fact that epistemic luck exists does not imply that true moral luck is justified.