South By North Strategies, Ltd.

An article in The Washington Post explains the hidden cost of tax expenditures:

Congress last cleaned up the tax code in 1986. Since then, special breaks have proliferated with bipartisan support and now permeate almost every corner of American life. The tax-free treatment of employer-paid health insurance will cost the government $160 billion this year, according to the Treasury Department. The tax break for mortgage interest will cost $92 billion. And deductions for state and local taxes will take $34 billion from federal coffers.
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Republicans see tax breaks as a way to spur business investment and rein in the growth of government. Democrats use them to channel money toward social programs — low-income housing, assistance for low-income workers, college tuition and green energy. But analysts say many of the biggest tax breaks have a built-in tendency toward cost escalation, similar to the automatic, formula-driven growth of old-age entitlement programs.
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“Budget wonks rail about limiting entitlement programs like Medicare and Social Security, but a large and growing share of federal spending is off the radar screen,” said Leonard E. Burman, a tax policy expert at Syracuse University. “Tax expenditures are on autopilot.”