Progressively raising taxes only drives away investors and entrepreneurs. If your country is going to tax my business or personal wealth to bring me down to the common level, there's no incentive for me to strive to accumulate the wealth in the first place, or else I'd be better off moving country to somewhere with a better taxation system.
Wait, that doesn't sound right. First you're saying people will work harder because working harder nets you more money, then you throw a fit about progressive taxes. Allow me to demonstrate the inconsistency trough an example:
Let us first define a variable called "work rate" or W, which entails the level at which you work, the value of what you do and how hard you work.
If there is a standard tax tariff of 10% and how much I make, not counting taxes is given by 1.000*W, then my net income is 900*W. To make 10 million dollars I have to attain a work rate of approximately 11 000.
Now imagine the case where the taxes are progressive so that everything I make over 1 million is taxed at 50%. So up to 1 million my income is equal to 900*W and further my income is equal to 500*W. If I now want to make 10 million dollars, I would make 1 million dollars in the lowest scale, for a W of 1 100, and the other 9 million I would make in the higher scale, which would take a work rate of 18 000, for a total required work rate of approximately 19 000, meaning you need to work at a rate of 8 000 higher to get that 10 million, or in other words an incentive to
work harder then if there was no progressive tax.
This should logically mean that progressive taxes
increase the incentive to work hard, because you need to work harder to get the same amount of money you would get if there was a flat tax rate. Similarly, anything that benefits people that make a lot of money would make it easier to get more money for those that are already rich,
decreasing the incentive to work hard for those that already make a lot.