The Senate passed a non-binding (more’s the pity on the “non” part) resolution to have the CBO score tax proposals dynamically in addition to its traditional—and utterly misleading—static scoring methodology.

Static scoring assumes the idiocy of, as The Wall Street Journal put it, that

people work nearly as much at a 60% income tax rate as they do with a 30% rate, and investors don’t care all that much if the tax on capital gains is 15% or 30%.

“This often leads to crazy results.”  You betcha [emphasis in the original].

In January 2003, for example, the modelers predicted that capital gains revenues would be $68 billion in 2006 and $73 billion in 2007.  In May 2003 Congress cut the capital gains tax rate to 15% from 20%, and in its revised budget forecast in August 2003 CBO estimated that the rate cut would reduce revenues to $65 billion in 2006 and $69 billion in 2007.

CBO wasn’t even close.  Actual capital gains revenue rose despite the lower tax rate to $109 billion in 2006 and $126 billion in 2007, thanks to faster economic growth and a greater incentive for investors to cash in their gains at the lower rate.

But here’s a larger problem.  The opinion piece then goes on to say

Tax reform done right should be revenue neutral using standard CBO static analysis, but a dynamic model would predict a large revenue windfall from the overall increase in investment and economic efficiency.  As part of a budget deal, those extra tax dollars that Democrats crave could be earmarked for deficit reduction.

That’s certainly a fine use of the windfall, but why, exactly, must tax reform be revenue neutral—statically or dynamically scored—in order to be “done right?”

The political imperatives involved for neutrality are painfully obvious, so that can’t be what the WSJ was talking about; let’s leave that aside.

Why, indeed, must tax reform be revenue neutral?