Both reactions are justified, of course, although we should be in no doubt as to which should take precedence. We should welcome such generosity whole-heartedly. It is not just the children's vaccines programme: Mr Gates gave $200m last year to link schools in poor American neighbourhoods to the Internet, and four years ago he set up the William H Gates Foundation, to give to education and health-care charities.
Our second reaction should be to reflect on the strong culture of philanthropy in America. Ted Turner's announcement last year of a stunning $1bn donation to the United Nations, in 10 annual instalments of $100m, was hailed as heralding the return of the Great American Benefactor. Indeed, the GAB had never really gone away. There is a much stronger expectation in America than in this country that the rich should engage in acts of heroic altruism. Much of the artistic and social fabric of America was constructed at the turn of the century by the giants of an earlier age - Andrew Carnegie, John D Rockefeller and Henry Ford. Carnegie's belief that "the man who dies rich dies disgraced" still holds sway.
And it is not just the super-rich, as one commentator noted: "It's difficult to walk into any American university, library, hospital or sports centre without seeing every brick of it named after someone or other." In the United States, 2 per cent of personal income is donated to some public- spirited cause or other, which is considerably more than we British manage.
However, a healthy amount of cynicism is perfectly justified. While the total level of giving in the US is impressive, the share accounted for by the very rich is relatively small. Carnegie's $350m at the beginning of this century was worth far, far more than Mr Turner's $1bn at the end of it. This week's donation represents just a quarter of 1 per cent of Mr Gates's $40bn total worth. At least he has promised to give nine-tenths of his wealth away eventually, and should be praised unstintingly if he does.
British philanthropy is a poor cousin, and not just because the British are poorer. Although there have been plenty of famous British benefactors - Rowntree, Nuffield, Tate - the urge to pass wealth to your children tends to outweigh the urge to give it away. One of the differences is the tax system. In America, charitable donations are tax-deductible. Here, you have to covenant your money over four years to qualify for income- tax relief, or donate through approved employer schemes.
But the tax system reflects, more than it promotes, the different culture in the US. So far, the Prime Minister's attempt to change the culture here has been fitful. His call last year to "make this the Giving Age", is somewhat undermined by New Labour's emphasis on business success rather than on the beneficial use of the fruits thereof.
Equally, Tony Blair's rhetoric is big on the responsibility of the unemployed to make best use of the state help they are given, but rather less big on the responsibility of the rich to return something to the community. One of the arguments of the Thatcherite Right used to be that British philanthropy had been killed by high tax rates on personal income, which substituted compulsory egalitarianism for individual generosity.
That argument does not apply now, and Mr Blair should make it more forcefully clear to his rich friends that a top income-tax rate of 40 per cent implies an obligation to use what is left for the good of all.
Income-tax relief on our charitable giving is a good idea - provided that the definition of charity is modernised to exclude privileged education.
The Giving Age was a fine phrase. If Mr Blair can help turn it into an even finer reality, that would confound the cynics.Reuse content