Tax increases historically have brought in far less revenue than predicted, as people change their behaviors to compensate. For example, when I was in England, people drove around company cars rather than owning them personally. It was explained to me that this was the result of tax rates - the high personal tax rates caused businesses to offer perqs which were not counted as income subject to tax. Hence the company cars.
...or a terrible example of unintended consequences. Employer-provided health insurance obliterated the individual market which has arguably brought less liquidity and less dependability to insurance, and with it less innovation to the economy as a whole...
