From Paul Krugman's New York Times op-ed column: "Isn't keeping taxes for the affluent low also a form of stimulus? Not so you'd notice. When we save a schoolteacher's job, that unambiguously aids employment; when we give millionaires more money instead, there's a good chance that most of that money will just sit idle."
Two points in response. First, the claim that the money of millionaire just sits "idle." That's ridiculous. Most millionaires don't keep money in their mattresses. They spend it on cars and houses and private jets and yachts. They invest it in corporate stocks and bonds or in venture capital funds or in private equity funds or real estate partnerships that build businesses that create employment and growth. They deposit the money in banks that make loans to businesses and homeowners. They buy government bonds that fund government spending. The money isn't going to sit idle whether taxes are high or taxes or low; the only question is whether the money will be allocated by private individuals or by politicians.
Second, the formulation, "we give millionaires more money." This assumes that the money belongs to the government, or society, in the first place, rather than belonging to the person who earned it. And it assumes that allowing a person to keep the money he earned constitutes a "gift" from the government. What a peculiar notion of property rights.