Most politicians think that simply raising tax rates will produce more Revenue. But, this simply is not always true. As taxes rates increase people are less likely to buy and at a critical point the actual revenues decrease - the purchases fall off faster than the tax rate increases. This is know as the Laffer Curve.
This is merely an example: A product sells for $10. It produces the most revenue at a tax rate of 20%. At lower tax rates the quantity sold is higher, and a higher tax rates the quantity sold is lower, but either way produces LESS Tax Revenue.