Robert Reich in the NYT has a really good graphical summary of the historical trends in the U.S. economy. If there's any doubt in your mind that the U.S. is a stronger country when top marginal tax rates are higher, this should dispel it. This is about as close to a controlled experiment as you can get in macroeconomics.
Be sure to scroll all the way down, and pay particular attention to the middle of the chart, where the results are neatly summed up in one sentence:
"Great wealth for the top 1% was reversed by policy but then rose again." (Emphasis added.)
What Reich doesn't say, but I will, is that it rose again because of government policy. The chart makes an unfortunate concession to physical layout by putting the white line that separates the "great prosperity" from the "great regression" around 1978. But in fact if you look at the income disparity chart, the real divergence between the top 1% and the rest of the population didn't begin until about 1982, shortly after the Reagan tax cuts. That's either an extraordinary coincidence (one of these day's I'll do the math and figure out the actual odds), or there's a causal relationship.
The evidence could hardly be clearer: low marginal tax rates on top earners leads to massive income inequality, which leads to a collapse in demand, which leads to economic depression. At root the problem is, as I have been saying for a long time now, a fundamental failure at all levels of society to understand the difference between money and wealth, and in particular, a widespread belief that having more money is the same as having more wealth. It isn't. The end-game of our current trajectory is the devolution of the United States of America into a third-world country, complete with crumbling infrastructure, inflated currency, and ubiquitous poverty except inside the gated enclaves of the rich and powerful. Of course, these things take time -- decades -- to play out. But unless We (or perhaps I should say You) the People take steps to reel in the emerging American oligarchy, there is no reason to believe that it won't play out the same way it did the last time we did this experiment.
To paraphrase Yogi Berra, it's 1932 all over again.