R1 Op cited an article from The Cato Institue by an author who "plays a key role in the libertarian movement" and called it "Economics for Dummies" . The author (who doesn't seem to have a degree in economics) attempts to cast aspersions at all of Keynesian Economics. He talks about the success of "supply-side" economics in the 80's and how the great Regan destroyed the evil Keynes and then attempts to label all economist who believes in Keynesian concepts as liberal. You won't find many economists who don't think investor expectations don't affect investments. He then brings up 8 points why the income tax should be cut.
1. In a free country, money belongs to the people who earn it. The most fundamental reason to cut taxes is an understanding that wealth doesn’t just happen, it has to be produced. And those who produce it have a right to keep it. We may agree to give up a portion of the wealth we create in order to pay for such public goods as national defense and a system of justice. But we don’t give the government an unlimited claim on our money to use as it sees fit.

While this idea does have merits, he seems to heavily underestimate the effects of capital deepening by projects like the American Freeway System and research from programs like DARPA. These projects and many others have greatly increased American wealth.

1. Private individuals and businesses use money more efficiently than governments do. People with their own money at risk spend or invest it carefully. You don’t find many $600 hammers or insolvent retirement programs in the private sector. Money will do more good for more people in private hands than in government hands.

This is not always true. Due to the economics of scale, it is sometimes a lot more economically feasible for the government to run programs. This is especially true when having to deal when there is no barrier to entry or negative externalities.

1. High taxes discourage work and investment. Taxes create a “wedge” between what the employer pays and what the employee receives, so some jobs don’t get created. High marginal tax rates also discourage people from working overtime or from making new investments. It’s true, as some critics say, that our current marginal rates of 39.6 percent (somewhat higher when combined with other taxes) do not depress economic output as much as the 70 percent rates that taxpayers faced in 1980. But most economists now agree that a reduction in marginal tax rates will increase output to some degree.

We know Y = C + I + G both G and C are the same, moving one to another has no effect. Countries with higher rates of taxes of the US produce the same amount per capita as the US. Northern Eurpeon Countries have higher GDP per capita but have a higher tax rate https://en.wikipedia.org/wiki/List_of_countries_by_GDP_(nominal)_per_capita

1. If we don’t cut taxes, Congress will spend the money. If one thing is certain in Washington, it is that Congress will spend every dollar it can get its hands on. Every interest group wants something—a road, a dam, a social program, more teachers, more policemen, more corporate welfare—and members of Congress want to be liked. The only way to “put the surplus in a lockbox” is to let the taxpayers keep it.

Using the tax revenues to close the national debt and invest in infrastructure or research could be a good thing.

1. Lower taxes are the only real check on the expanding size and scope of the federal government. If we want smaller government, our best strategy is to reduce the amount of money Congress has to play with.

This is an ideological based argument and could hurt the money fiscal multiplier. Government spending should be based on what gets the best fisical multiplier.

1. For Bush and Republicans in Congress, this may be the most important reason of all: Republicans win when they cut taxes. Tax cuts unite the Republican base. The tax consumers in our society are well organized; the taxpayers need to be organized, too, around a tax cut program. In 1980, 1984 and 1988, Ronald Reagan and George Bush won three presidential elections by promising to cut taxes and then cutting them. George Bush raised taxes and lost the next election. I wager this is a lesson not lost on George W. Bush.

The Bush Administration tried to have their cake and eat it too. They cut taxes and increased spending, this led to large needless deficits. For me personally, this killed the idea of "fiscally conservative" of having balanced budget and spending wisely.