When you bunch up all the taxes we pay, including Income Tax, sales tax, property taxes, social security, etc. we all end up paying very similar amounts (up around 30-40%). The overall tax structure is incredibly complicated, which is part of the problem, and the answer is not an easy one. We are not a country for the most part that wants to let people die of hunger in the streets. If we tax people to the point that they can not meet their needs than we as a whole have to meet that need. Also, it seems to me that people who make less money tend to spend larger percentages of what they do have, which helps to drive the economy. I think these two reasons are partly why most developed nations have a progressive tax system. What is fair is what is best for all of us.
Personally, I think that if you look at things like the rise in CEO pay and the growing disparity of income between the wealthy and the poor, it would suggest that the wealthy for whatever reasons are doing too well. Many people believe this is because the system is unfair, but in the advantage for the already wealthy. I tend to agree. Actually, I more than tend to agree. I'd be perfectly fine if the top tax brackets were doubled (along with minimum wage).