It seems true that when investing, you're trying to get the highest return possible, in terms of a single value measured in currency.

I've never understood why it should also necessarily be true with charity. It seems often to be an unexamined assumption, and may be reinforced by using terminology like "utilons" that appears to be begging the question.

Someone who donates both to the mosquito nets effort in Africa, and to the society which helps stray dogs and cats in Michigan, is not necessarily being irrational. They just may be perceiving the two benefits to lie on incomparable axes. They may be caring about helping Africans and helping stray dogs simultaneously, in different ways that are not exchangable to each other. The familiar objection is: "Sure they are exchangable; everything is exchangable into utilons; if you don't see a clear rate of exchange for your own preferences, that just means you still ought to estimate one given your imperfect knowledge, and act on it". But I don't see why that should be true.

Certainly most of our spending is done on axes that are incomparable to one another. We have needs along those axes that we do not normally consolidate to one "most efficient" axis, even after the minimal requirements are met. Investing is the activity that's the odd one out, here - and one of the reasons it is is precisely that we don't care much which of the companies we invest in brings us profit. It seems odd that charity should so unequivocally stand along with investing as an exception.

If charitable giving is not an exceptional way for us to spend money, the idea of a single currency becomes difficult to support, because if charity must be so streamlined, why not all other activity? In other words, sure, you can criticize someone for helping stray dogs by saying their money could be saving lives in Africa instead; but is that very different from criticizing them for buying a large color TV, when their money could be saving lives in Africa instead?