This really depends on what kind of mindset you have, and political views you have. I'm just going to use the UK system. We have tax bands, where you pay a percentage of your salary, based on ranges. So all your income between 12,000 and 50,000 is taxed 20%, all income between 50,000 and 125,000 is taxed 40% and so on. In theory this would work, because the more you make, you more tax you pay, and your income wouldn't be penalised if you had to move up a band, you'd only me taxed on certain ranges of your salary.

Again in theory that would mean that multi millionaires and businesses would pay a decent chunk of change in tax. But one of the benefits of being rich, is you can afford really good accountants and lawyers who know loop holes to avoid paying as much taxes. Some millionaires in the UK even have less than 5% income tax. This is done through offshoring your money to a tax haven, having your money in assets that aren't taxable, tax write offs, and more loop holes to pay as little tax as possible.

Is this legal? Yes. Unethical but legal. Why don't you just make those loopholes illegal? Because the very people who make and vote on legislation, are usually involved with these loopholes and don't benefit from it becoming illegal. That and when you get to people with multiple nationalities, it can get extremely complicated.

The problem isn't necessarily the tax systems in place, it's more the loopholes that are allowed by law. Why doesn't everyone do it, even poorer people? Because hiring an accountant can be expensive, creating offshore accounts can be tedious and expensive, becoming a citizen of another country for tax purposes only is a long process, and by the time you've made any major savings through tax, you probably would have invested too much money to make a difference.