That said, I don't think that a moral obligation needs to be framed - or should be framed - by necessity as "a precept which overrides all other behavior". One shouldn't put too much of restraint on that, else one will by necessity end up with disfunctional morals. A moral obligation can be weaker than that, and the obligation should be in proportion to the value it's connected to.
Also, even if we constrain moral obligation like that: The fact that human beings won't in most cases behave like the moral obligation does, doesn't devalue the moral obligation. It'd be a fallacy to say that what ought to be needs to be. As there are some poeople who give everything they don't necessarily need even such a constrained concept of the moral obligation to prevent others from starving is possible to fullfill. So, the argument that the moral percept isn't possibly fulfillable has no traction. That it isn't particularly useful is more a symptom of unreasonably constraining what a moral obligation is.
Two things.
First, by definition, a moral
obligation is a demand to put aside other priorities to effect some action. It isn't a requirement to refrain from action, or to possibly take action, it is imperative, i.e., obligatory. If it isn't obligatory, than it isn't a moral
obligation, is it?
It is certainly possible to uphold varieties of moral
values or
goals, but these things are, by necessity, somewhat looser than obligations. For example, I could hold the moral goal of seeing people not starve to death, but that does not obligate me to a particular action. It merely means that, of the several goals I have, I will not act in such a way as to make starvation more likely. It may mean that I act positively to end starvation. But because it is a goal, rather than an obligation, I am not forced to devote all ends towards ending starvation.
Second, the fact that some people can act in such a way as to fulfill an obligation does not mean that said obligation is a reasonable creation. It is true that a person can act to devote themselves entirely to the welfare of others. The difficulty with this arises when we examine the results of everyone living up to this moral obligation. If most people were to be devoted to the welfare of others, vast inefficiencies would form (you don't know what is good for me as much as I do), free riding would become the optimal survival strategy, and trade, capitalism, and technological progress would grind to a very rapid stop. If mankind continued to follow this "moral obligation", the only people left would be those who refused to go along with it. The obligation would self-annihilate. Actually, when we have tried to implement obligations like this, the societies tended to grind to a halt a long time before that.
Now, one can make the argument that morality has nothing to do with practicality. Perhaps so. But if it is so, then so much the worse for morality. If behaving practically, rather than morally, makes us all better off, wealthier, healthier, and etc, then there is no reason to be moral. Or, to put it otherwise, morality is only as useful insofar as it makes our lives better. To wit, perhaps it is immoral to tell any lie, as in the categorical imperative, but if I am hiding Jews in the basement, and Nazis are knocking on the door, then the categorical imperative can take a long fucking hike.
I am not very empathetic. Actually, I may not be, at all, since I'm not sure what empathy should be. Perhaps then, I am missing some key component of moral decision making. But it seems to me that, if one wants to consider matters of morality, one should not start with moral rules and work up to what we should do, but, rather, discard our impulses, consider what works best to create a better world with less suffering, and then construct moral rules from that. In the same way that we understand medical science, originating our theories on the basis of what is best for the patients (i.e., all of us) and then creating goals and rules for general behavior from there. That is understandable, objective, rational, and, hopefully, more workable.