The best defense I've heard yet for McCain's big tax flip-flop

Justin,
The problem with your comment is it is the equivalent of Bush jumped off the bridge therefore we should do it too. The simple truth is something my grandfather taught me many years ago. If money in is less than money out, you've got a problem. In this country, we really have double trouble, we have too little money coming in and too much money going out. This mathematical exercise is so simple any third grader could tell you how this works out.
-Bryan

I think it's more like Bush and the rest of us jumped off a bridge and now we're in the alligator-infested river below, but we might be better off swimming over to the river bank and walking up from there rather than trying to climb straight up the bridge supports. Although, given the alligators, maybe that's wrong. Definitely, though, if someone comes along in a boat, we should get into that. Dontcha just love metaphors?!?

I'm no Burkean either, so I don't understand why letting a bad tax cut expire would be a major negative shock to the economy. Would you mind explaining?

From Christina Romer and David Romer's "The Macroeconomic effects of tax changes:
Estimates based on a new measure of fiscal shocks":

[O]ur results indicate that tax changes have very large effects on output. Our baseline specification suggests that an exogenous tax increase of one percent of GDP lowers real GDP by roughly three percent. Our many robustness checks for the most part point to a slightly smaller decline, but one that is still well over two percent.

On the other hand ...

Finally, we find suggestive evidence that tax increases to reduce an inherited budget deficit do not have the large output costs associated with other exogenous tax increases. This is consistent with the idea that deficit-driven tax increases may have important expansionary effects through expectations and long-term interest rates, or through confidence.

The second portion of that argument that "suggestive evidence that tax increases to reduce an inherited budget deficit do not have the large output costs associated with other exogenous tax increases" has no real meaning. In real terms (maybe not perception wise), there is no difference between tax increase to cover past deficit spending, exogenous tax increase or the more magical McCain's merely "closing tax loopholes." Any of the three has the very real effect of taking moeny away from my neighbor and I.