Since the affluent tend to itemize their deductions more than do average taxpayers, and since the affluent pay higher marginal tax rates, they tend to benefit more from deductions. Ergo, limit deductions and you raise the effective tax rate (not the marginal rate) of the affluent. (The effective tax rate is the share of total income paid in taxes, while the marginal rate is the tax on the next dollar earned.) Such a reform would help tax efficiency and equity, and the economy would benefit from fewer investment distortions.
But suddenly liberals are having second thoughts, and our guess is that this is because residents of high-tax Democratic-run states are about twice as likely to take advantage of tax loopholes as taxpayers in low-tax states. For example, 44% of Connecticut filers itemize their deductions, but only some 21% of North and South Dakota residents do.