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.
That's interesting and I think that's true to a certain extent, the bottomless pits of suffering and all that. Though Kantianism does make some pretty strong demands in its own way, for instance in the way that it really hammers home the idea of seeing things from others' points of view (via the Formula of Humanity), or in the way that it considers some duties to be absolute ("perfect").
I believe that Korsgaard also thinks we have duties to help others' promote their own good if it's at no great cost to ourselves, though these duties are not as strong as those not to violate other people's autonomy. I think maybe these sorts of duties lead to something like Effective Altruism, though I haven't really thought all of this through yet, or read much of the relevant literature, so what do I know.