We can have a progressive tax rate that is simple. Unfortunately, people such as Grover Norquist make it extremely hard. They want our current tax system to be as complicated as possible so then they can say, "Hey! Let's just do a flat tax." Thus shifting the burden of taxes from the rich to the middle class. He actually raised heavy objections when California implemented the ReadyReturn system. [1]
[1] http://www.nbcnews.com/id/8134597/ns/business-motley_fool/t/...