Hello Pete, thanks for commenting.
I think it depends on how you define altruism. David Brooks (and many others) assume it is a form of selflessness, in which the altruist ends up in a “net worse” position after an altruistic act.
As I try to explain in my article, I do not subscribe to that view: when we do something for someone else, we do so because we get something in return (social capital, support for our genes, or simply a warm glow). So, giving money to charity is not really selfless, and therefore giving *more* money is not *more* selfless (and not altruistic in this sense).
You could argue that, even if you get more of a warm glow by giving more to charity, you would be more altruistic if you did so. But if – as I do – you don’t make a distinction between material benefits and non-material ones where trading is concerned, that would not be any different from someone selling ice cream who would be more altruistic if she sold *more* ice cream, even if she did so because she would earn more money that way.
Hope this clarifies!