One obvious issue with this argument: The claim that higher tax rates can reduce GDP is from Arthur Laffer and his Laffer curve -- and relates to the total tax burden, and not the marginal rate.
What would make a more reasonable comparison is if you compared similar US States with different tax burdens in over the same time period.
http://www.google.com/publicdata?ds=wb-wdi&met=ny_gdp_mk...
It'd be nice to figure out what datasets are available in the Public Data. That's really useful.
Most social sciences (including economics) can't very well be exact for the lack of experiments, much less controlled experiments.
It's impossible to accurately model the economy of a society, but theories like this can help politicians better judge the impact of their policies.