I am hardly the tax expert, but one difference I see between the likes of Romney and Lefty is income from wages earned and income from dividends and capital gains. While the income from wages is indeed progressive, the conservatives actually won a huge victory with the new tax laws which made the bush tax cuts on dividends and capital gains permanent. I see this system as indeed favoring the wealthy. The average mid-class American is only marginally invested in stocks and business ventures that would give lower taxed dividend and capital gain income relative to the wealthy. The conservatives, including Mitt, proposed closing some of these tax loopholes to increase revenue but unfortunately never came up with the specifics that might have expedited this.
The concept that progressive personal income tax rates stifles economic prosperity just doesn't fly with me. The rates on higher incomes are at historic lows and times of higher tax rates for the wealthy have gone hand in hand with times of economic prosperity. What does stifle growth is the burgeoning federal debt and the interest burden on that debt. The only practical way I see to reduce debt and balance the budget in the balanced approach of spending reductions and tax increases. This would help to preserve the integrity of SS and medicare, and also provide income for infrastructure improvements and sustainable energy development. While the concepts of a flat tax and huge military cuts are enticing concepts, practically speaking I just don't see these happening. What seems more likely to me is the closing of tax loopholes that mostly favor the wealthy.
Actually, Lefty is from California, where they recently achieved a balanced budget. And state tax increases were a big part of that.