M. writes: How does a Stoic judge the limits of what they ought to do in a situation where theoretically they could have a great influence if they used all their resources or even sacrificed themselves? Any of us could intervene to greatly improve the life of a person in crisis, and such people aren't hard to find. But how should that be weighed against however one would prefer to use one's life or resources for? And how are we to judge when we cannot know all the consequences an intervention may have?
As an extreme example, in Romeo Dallaire's book "Shake Hands with the Devil" he describes how he could have shot some of the central perpetrators of the Rwandan genocide while it was ongoing. In his role as commander of the UN force he met with them while armed. He says in the book: "I had tried to anesthetize myself to the ethical and moral dimensions of meeting with the genocidaires, recognizing that if they refused to assist in the transfers I might not ever get anyone out. Arriving at the hotel, I took the bullets out of my pistol just in case the temptation to shoot them was too extreme, and went inside."
I don't think it's as simple as saying that he was wrong not to kill them just because it would have been illegal (whatever that might have meant inside mid-genocide Rwanda) or would violate his role as a UN peacekeeper or a Canadian soldier. It's certainly of practical relevance that the action would have led to him being relieved of command and perhaps criminally tried, though under the circumstances perhaps politics and questions about his mental state would have prevented the latter.
How are we to interpret extreme situations like that -- but also the everyday occurrence of walking past the sick, possibly unconscious, possibly dying person in the subzero Toronto street -- within the tenets of Stoicism?
The best resource that Stoicism has to address these questions, in my mind, is Epictetus' role ethics. I will elaborate in a moment, but first let me comment on a few of your specific points.
One of your early questions is: how are we to judge when we cannot know all the consequences an intervention may have? Exactly. That is one reason I am not a Utilitarian. Utilitarianism says that we ought to try to maximize most people's happiness, whatever "happiness" means. It is a type of consequentialist moral philosophy, meaning that the only criterion that matters in order to judge whether an action is good or bad are its consequences. But as you say: how do we reasonably establish such consequences? How far into the future do we have to look? Utilitarians do not provide us either with a reassurance that we are often in a position to make reliable predictions about the consequences of our actions, or with a logically consistent stopping point for how far down the line we need to look. It's hopeless, in my view. This is not to say that virtue ethics -- of which Stoicism is an example -- doesn't care about possible consequences, a common misconception, unfortunately. It's just that the focus is on the intentions of the agent, accompanied by the acknowledgment that while intentions are up to us, outcomes are not: we may, in good faith, act in a certain way in order to bring about a desired outcome, but Fortune may get in the way and thwart our plans.
Second, you say that Dallaire's case does not boil down to just saying that he was wrong not to kill the chief perpetrators of the Rwandan genocide because it would have been illegal, or because it would violate his role as a UN peacekeeper or a Canadian soldier. I agree. If we clearly see that a certain course of action is ethical, that supersedes the law. That is for the obvious reason that laws are sometimes unjust, or that lawmakers might not have foreseen the particular situation in which we happen to find ourselves at the moment. Of course, we need to be very careful when contemplating whether to sidestep the law, as there is the constant danger of rationalization. I think we should also be willing to take responsibility for our actions: if we willfully violate the law for reasons we think are ethical, then we should have the courage to face the legal consequences, making our case publicly in a court of law. This, as you might imagine, is easier said than done, but such willingness to face consequences does tend to counteract our tendency to rationalize our own motives. The classic example is Socrates, who faced the unjust accusations against him in the Athenian court, and refused to escape from prison -- which he could have easily done. Or think of Rosa Park, in recent American history.
Now to the crux of your question: what are the limits of our responsibility toward others? The broad Stoic framework is one of cosmopolitanism: we have duties toward every other human being, precisely because they are human beings, that is, social creatures capable of reason, interconnected with us by the web of cause-effect. This, per se, doesn't settle the question of limits, though. To get there, we need Epictetus' role ethics.
In various places in the Discourses, Epictetus articulates a view according to which we have a universal role, as human beings, and a number of more limited roles, for instance as parents, sons or daughters, friends, co-workers, and so forth. The first consequence of this structure of roles is that we are justified in focusing on our local roles on the basis that that is where our agency is maximized. I can do comparatively little, say, about stopping an ongoing genocide on the other side of the world. But I can do much for my family, my friends, my students, my colleagues, and so forth. So long -- and this is crucial -- as none of my actions when I take on my various individual roles go against the interests of the human cosmopolis. For instance, if in order to help my daughter get her career going I have to act unjustly, by bribing someone into giving her a job, I am betraying both my own character and the notion of justice. My daughter will have to further her career by ethical means, and the scope of my support will also be ethically bound.
That said, both in terms of local and universal roles, some people may be willing or able to do more than others. Epictetus discusses some examples in Discourses I.2, aptly entitled "How may a person preserve their proper character upon every occasion?" The first example contrasts the reaction of two senators, Florus and Agrippinus, to a request by the emperor Nero -- whom the Stoics saw as a tyrant -- to make an appearance at a public festival:
"When Florus was debating whether he should enter Nero's festival, so as to make some personal contribution to it, Agrippinus said to him, 'Enter.' And when Florus asked, 'Why do you not enter yourself?' he replied, 'I? why, I do not even raise the question.' For when a man once stoops to the consideration of such questions, I mean to estimating the value of externals, and calculates them one by one, he comes very close to those who have forgotten their own proper character."
The point is that both senators opposed Nero, but one was willing to consider appearing in a festival designed to glorify the emperor, while for the other the question wouldn't even come up. Perhaps Florus feared retaliation against his family, or had some other good reason to compromise his integrity. We don't know. It is up to each of us to determine where to draw the line. The second example recounts a dialogue between another senator, Helvidius Priscus, and another tyrant, Vespasian:
"This is what Helvidius Priscus also saw, and, having seen, did. When Vespasian sent him word not to attend a meeting of the Senate, he answered, 'It is in your power not to allow me to be a member of the Senate, but so long as I am one I must attend its meetings.' 'Very well then, but when you attend, hold your peace.' 'Do not ask for my opinion and I will hold my peace.' 'But I must ask for your opinion.' 'And I must answer what seems to me right.' 'But if you speak, I shall put you to death.' 'Well, when did I ever tell you that I was immortal? You will do your part and I mine. It is yours to put me to death, mine to die without a tremor; yours to banish, mine to leave without sorrow.'"
Obviously, Helvidius held his own behavior to a very high standard, openly defying the emperor, even under a direct threat of death. A threat on which Vespasian did follow through, incidentally. Near the end of Discourses I.2, Epictetus directly addresses your question, so I'll leave the last word to him:
"Only consider at what price you sell your freedom of will. If you must sell it, man, at least do not sell it cheap. But the great and pre-eminent deed, perhaps, befits others, Socrates and men of his stamp. — Why then, pray, if we are endowed by nature for such greatness, do not all men, or many, become like him? What, do all horses become swift, all dogs keen to follow the scent? What then? Because I have no natural gifts, shall I on that account give up my discipline? Far be it from me! Epictetus will not be better than Socrates; but if only I am not worse, that suffices me."