...and the same is true if his philanthropy leads him to work full-time at a nonprofit instead of going to law school to become a lawyer who makes $1,000 / hour in the first place. Unless it's one HELL of a nonprofit.

The Roman historian Sall.u.s.t said of Cato "He preferred to be good, rather than to seem so". The lawyer who quits a high-powered law firm to work at a nonprofit organization certainly seems like a good person. But if we define "good" as helping people, then the lawyer who stays at his law firm but donates the profit to charity is taking Cato's path of maximizing how much good he does, rather than how good he looks.

And this dichotomy between being and seeming good applies not only to looking good to others, but to ourselves. When we donate to charity, one incentive is the warm glow of a job well done. A lawyer who spends his day picking up litter will feel a sense of personal connection to his sacrifice and relive the memory of how nice he is every time he and his friends return to that beach. A lawyer who works overtime and donates the money online to starving orphans in Romania may never get that same warm glow. But concern with a warm glow is, at root, concern about seeming good rather than being good - albeit seeming good to yourself rather than to others. There's nothing wrong with donating to charity as a form of entertainment if it's what you want - giving money to the Art Fund may well be a quicker way to give yourself a warm feeling than seeing a romantic comedy at the cinema - but charity given by people who genuinely want to be good and not just to feel that way requires more forethought.

It is important to be rational about charity for the same reason it is important to be rational about Arctic exploration: it requires the same awareness of opportunity costs and the same hard-headed commitment to investigating efficient use of resources, and it may well be a matter of life and death. Consider going to GiveWell.org and making use of the excellent resources on effective charity they have available.