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If top marginal income tax rates are set too high, they discourage productive economic activity. In the limit, a top marginal income tax rate of 100 percent would mean that taxpayers would gain nothing from working harder or investing more. In contrast, a higher top marginal rate on consumption would actually encourage savings and investment. A top marginal consumption tax rate of 100 percent would simply mean that if a wealthy family spent an extra dollar, it would also owe an additional dollar of tax.

Source: bobmorris.biz
If top marginal income tax rates are set too high, they discourage productive economic activity. In the limit, a top marginal income tax rate of 100 percent would mean that taxpayers would gain nothing from working