When people want to complain about taxes, they'll talk about the
top tax bracket rate, and how high it is.
The current top US Federal
marginal rate for personal income tax is 39.6% as of 2016. This sounds huge.
But actually no one pays that rate!
For starters, the marginal rate for a particular bracket is
only paid on the money in that bracket. For example, the rate on the lowest
bracket is 10%, up to $9,225 for a single person. Even someone with
a million dollar income only pays 10% on the first $9,225 they
make. The 39.6% rate is only used on the amount they make over $413,200.
(There are a bunch of other rates in brackets in-between these two.)
In addition, the various deductions and exemptions mean that a lot of your income doesn't get taxed at all.
You can demonstrate this to yourself by calculating your own personal effective tax rate. Look at the actual amount of Federal taxes you paid last year, and divide it by your actual total gross income. I make a decent amount of money, but my effective Federal income tax rate is only 11%, barely higher than the "official" minimum rate.
Similar comments apply to supposedly high corporate tax rates: you have to look at the effective tax rate companies pay.
This doesn't mean that simplifying the tax code is a bad idea.
But any net lowering of taxation won't produce a big effect, because
the effective rates are already not very high.