My two cents worth.
It all depends on what behavior model you have for investors and their expectations. Right now a lot of commercial real estate deals are trying to close by the end of December under the assumption that capital gains rates will rise in 2013. To the extent that some of this real estate is underutilized now and will be more aggressively utilized by the buyers, the anticipation of future higher capital gains rates may be marginally promoting economic growth. But this is a temporary effect and in general it is hard to see how with very low rates of anticipated inflation and low real interest rates that raising capital gains rates is helpful to the economy.The notion that a higher CG rate can possibly be a positive for economic growth is nonsense.
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That's the Obama model of economics. Cram future demand into the present and hope for the best. The umbers this year look better probably because a lot of people are taking gains and making use of Bush-era tax rates in anticipation of next year being worse. But that only robs from the future for today. It isn't sustainable at all.