Greg Mankiw writes:
I have a plan to reduce the budget deficit. The essence of the plan is the federal government writing me a check for $1 billion. The plan will be financed by $3 billion of tax increases. According to my back-of-the envelope calculations, giving me that $1 billion will reduce the budget deficit by $2 billion.
Now, you may be tempted to say that giving me that $1 billion will not really reduce the budget deficit. Rather, you might say, it is the tax increases, which have nothing to do with my handout, that are reducing the budget deficit. But if you are tempted by that kind of sloppy thinking, you have not been following the debate over healthcare reform.
Charles Krauthammer makes the same point less sarcastically. He then goes on to point out that the idea is even stupider than that, because all the numbers are rigged.