I, and presumably you, can not even worry (though we might not like it) if they take 20% of our income. If you take $2000 out of $10000 that's must more painful than taking $20,000 out of $100,000.
If the subject is a business, it's actually pretty easy to avoid making much of a profit at all. For example, if you own your own business then just pay yourself a salary and pay the taxes on that. The business isn't taxed, really, you are. To the IRS, that's a legitimate business expense. Open a new office, give folks a raise, or whatever and those become expenses and the profit is less... Then, well, you add in depreciation and all sorts of things - it gets pretty damned complicated.
Which leads to this: Those who can better afford it are more able to take advantage of the loopholes. I don't think it's possible to set up a tax system that does not have potential for abuse. Sadly, those who can benefit the most are the least able to afford the professionals to do their taxes. I recommend everyone hire an accountant and pay a lawyer, and I recommend that they consider incorporation, but many people can't justify the expense. Oddly enough, they probably *could* justify the expense (in many cases) based on how much they'll save but many folks don't seem to look at it like that.
Finally, I've said this before but I think it bears repeating, I don't think my government has an income problem so much as it has a spending problem. I have no problem with the amount I pay in taxes and could easily bear a higher tax burden but I'm not just going to give it to them so long as I can (legally) avoid it. We've got enough bombers, aircraft carriers, and tanks.