To an extent, certainly you must tax people who make more money more in order to generate governmental revenue. It's simple mathematics--the poor don't have the money to tax, and some services are necessary for a country to actually function at all.
The question becomes, where is the appropriate balance? Many factors affect the proper amounts to levy. Increased taxes generally decrease employment and overall productivity--the multiplier effect, when applied to the lesser cash flows after taxes, means that less money is being turned into goods and services. Yes, you can make the argument that the government is increasing employment and sort-of increasing overall productivity based on that tax revenue, but let's be serious now, the government has never and will never be a competitive employer. The more people the government employs, the harder it is for market companies to employ people, for a host of reasons. The government has no real drive to innovate, no drive to perform optimally and run the leanest, most effective machine it can--only to self-perpetuate. Giving them more money to do so strikes me as foolishness.
There are also ethical and moral questions raised by taxing the middle-class. (The "rich"--that is, having the proverbial fuck-you money--starts in the multiple millions; they are being taxed higher, but they are certainly not the only ones.) I see significant moral hazard in taxing the haves in order to provide shinies for the have-nots--not because of greed, but because the people giving the have-nots said shinies are doing it in order to get re-elected rather than because they actually care. Benefits to the people are a side effect at best.