Ryan's $34 Trillion Tax Folly

David Cay Johnston | May. 9, 2011 09:31 AM EDT

If repairing your car cost 18 percent of your income, would you buy a new car? Of course you would.

Now imagine that your mechanic tried to persuade you to keep the jalopy with a clever tax argument: The costs of your annual car tax and registration would decline over time, saving you money. Keep the car long enough and you would save a third of a year's income just in taxes.

That sounds appealing, unless you stop to think about how much more you would pay for repairs as your vehicle ages and breaks down ever more often.