First its important to remember tax in a "progressive" system, is not for the benefit for the people paying the tax.
This makes sense in the fact that people who have more money, have more money that can be taxed.
It doesn't make sense in terms of the people who get taxed, have no say in how much, when and who it goes to.
Income tax specifically gets taxed at the point you are paid, and gets taken off the total by the employer. There are two main problems with this:
Income tax is assessed on a 12 month rolling basis. In terms of fairness this would be no problem if the tax rates were the same from period to period, and your income tax bands stay constant between periods. But this is not the case in a progressive system.
A set of twins embark on two different careers. One works in a bar from age 18 at a salary of 18,000/year and the other goes to university to become a lawyer, graduating 4 years later with a salary of 30,000. The tax rate is 10% for earnings under 20,000 and 30% for everything after.
In year 8, both of the twins have earned 120,000, but one has paid 66% more tax than another???
What's worse, is that twin had to borrow their way through university, making them poorer still than the other twin.
If the situation continues, the one who has paid more will pay even more than the other still.
If in year 9 the lawyer, decides they hate the lawyering business and they wish to become a barrister and earn 18,000 a year, they will have paid more tax for no real justification.
Fairness of tax http://www.bbc.co.uk/news/uk-politics-19406022