Christine M. Korsgaard was kind enough to answer a few questions of mine. Here's an excerpt:
ERICH: I have the impression that some utilitarian philosophers are having an outsize impact on the world. I am thinking, for example, of Singer, Toby Ord, William MacAskill and Hilary Greaves who have been instrumental in founding the Effective Altruism movement, which is having a large impact on global poverty and health, factory farming and so on. Is this a correct observation, do you think? If so, is it something about utilitarianism that spurs concrete action of this sort? And does Kantianism not?
CHRISTINE: The idea of doing a lot of good has a lot of appeal. The Effective Altruism movement also appeals because of its focus on good you can do right now, and as an individual, at least as long as someone else is doing the complicated work of organizing the charity and distributing the proceeds effectively. The problem of global poverty requires a political solution; charity, no matter how extensive, can never be more than a band-aid. But it does have immediate results. I think utilitarianism has an advantage over Kantianism in the public sphere because it is, at least superficially, much easier to understand, and the theoretical problems with it that I described before are hard to see.
Thank you for the thoughtful comment! It is an excellent book – if you are at all interested in Kant's moral philosophy, I highly recommend it. I will preface the remainder of this comment with the caveat that I am explaining someone else's work, and that Professor Korsgaard may not agree with my interpretation. Also, any typos in the quoted passages are copying errors.
Here's a passage from the book that expands on that thought but doesn't counter your objection:
However, later on she gets to the argument from marginal cases (if something like intelligence or rationality is the ground for moral standing among humans, then what about infants, or folks with severe developmental impairments?), which I think is similar to your objection here. Korsgaard argues against it, because to her, there is such a thing as a type of creature, even if categories have fuzzy borders. And though your example beings may not be able to pursue their own functional goods, they are still the sorts of creatures who do.
Korsgaard is talking about rationality here because that, to her, is what sets humans apart from the other animals (though of course she thinks that is the reason why we are moral agents, but not why we have moral standing). But I think she would argue similarly about creatures that are defective in other ways, e.g. who has no power to control what they experience or to pursue goals.
If I understand you correctly, I think she would agree. Her distinction between "final goods" and "functional goods" comes, I think, from this 1983 paper of hers, though there she calls functional goods "instrumental" instead. The functional good is basically that which allows a thing to function well, e.g. a whetstone is good for the blade because it keeps it sharp and tar is good for the boat because it keeps it from taking in water. The final good is "the end or aim of all our strivings, or at any rate the crown of their success, the summum bonum, a state of affairs that is desirable or valuable or worth achieving for its own sake". Where does the final good come from? Korsgaard basically argues, if I recall correctly, following Aristotle, that creatures have functions, and that, when we act to achieve some end, to attain whatever we value as good-for us, we take that end to be good in the final sense. I think this is pretty similar to what you were getting at?
Ah yes, I thought so too, especially since I had understood (mistakenly, apparently) from the book that she did not think of those things as ends in themselves. I actually wrote a dialogue in the old style about this very subject, concluding that inanimate objects are not ends in themselves.