It would teach the world a lesson that America can’t be trusted. They are already pissed at us for freddie mac and a bungled $.
And why would that be? Nations around the world change their tax policies all the time. Apart from a small cadre of economists and central bank planners most people around the world, including investors, aren't really that concerned about the details of tax policy. Taking a close to home example, how concerned are you that the State of Massachusetts periodically has a sales tax holiday?
What really matters to people around the world is the general state of our economy, its growth rate, and what US consumers are spending. Investors around the world would much rather see a tax holiday here followed by a tremendous economic rebound than they would see some other stimulus attempt followed by years of depression, recession, or even just minimal GDP growth.
Why are you so afraid of a large tax cut?