And likewise, there is only one best charity: the one that helps the most people the greatest amount per dollar.

I disagree. Giving money to charity is not different from spending money on a latte at Starbucks. I spend money according to my values. And I still buy lattes. I am not Zachary Baumkletterer. Even Jesus said, "The poor you will have with you always", to justify spending an INCREDIBLE amount of money (enough to buy ten people's entire lives, in an era with no inflation, making it comparable to ten million US dollars today) on pouring perfume once on Jesus' feet. The guy was tired and depressed and about to be crucified and wanted his damn perfume, like I want my damn latte.

Similarly, people who gave money to keep a painting in a museum, might also spend considerably more money to buy paintings to hang in their houses, than it would take to save a life in another country. These people value art, and they value benefitting others. Draw a 2D plot, and label the axes "selfish ... unselfish" and "spiritual ... physical" ("spiritual" standing for art and other "impractical" values). One person might

• buy a painting to hang in their bedroom (spiritual, selfish)
• buy a painting to hang in their guest room (spiritual, sorta selfish)
• spend to preserve a painting in a museum (spiritual, unselfish)
• buy fuzzy slippers (physical, selfish)
• spend money for vaccines in Africa (physical, unselfish)

And each of those things could have similar utility for them.

I don't think this is irrational. Irrational is spending any money at all on "charity" instead of spending it according to your utility function.

This post contains the hidden presupposition that charity, using a collective utility function, is more moral than self-oriented actions; and therefore, following our utility functions is immoral. This is an assertion about morality and rationality that has huge implications! It is resonant with a very common meme that says that "moral" behavior is behavior that we don't want to do, because we are fundamentally immoral. I say, instead, that morals are part of our utility function - that we have these things called morals because part of us really wants to be nice to other people. They are just another part of our utility function.

Encouraging unselfish behavior can be done by manipulating peoples' selfish desires to produce "unselfish" behavior (give to charity and get social benefits, or stay out of Hell), as a mechanism to solve PD problems with a given payoff matrix. But it can also be done by treating people in ways that encourage what natural unselfish tendencies they have - solving PD problems by changing people's payoff matrices.

Apply Kant's imperative. This post suggests that we have 2 utility functions, one for everyday life, and another for charity; and that the one for charity is more moral. But if everyone used such a charity utility function for everything they did, it would result in a global race to the bottom as economies imploded after spending all national wealth on ameliorating suffering while undercutting all private motivation. Therefore, it is less moral. It is not only not obviously moral, it is immoral, if that means anything, for a government, or a person, to spend every last dollar on helping the unfortunate before spending any money on education, roads, defense, art, or even entertainment.