As one of my law professors used to say, it's okay if your heart bleeds, so long as it bleeds green! I submit that most who defend the current tax system either have so much money that it doesn't matter what rate they pay or make so little that it is fun to stick it to the "rich" guys.
I grew up poor/middle class and thought the tax system was fine. I went to college/graduate school/law school for 12 years so that I could get a good job that would allow me to support my wife and our future children without requiring her to work. I bought a house and contributed to many charitable causes, thinking that I would be entitled to nice deductions.
Well, guess what? The line between "rich" people who get screwed by the IRS and middle-class is much lower than most people realize. I have only been working for a few years, and already a sizable percentage of my itemized deductions are disqualified. In a few years, they will be gone completely! Maybe by then, I won't care (I will, of course), but right now it really pinches (between income tax, property tax, and sales tax, I paid over 50% of my income to the government this year).
It's easy to be self-righteous and indignant when you're sitting in the cheap seats, watching rather than playing. When you've just paid $80k in federal income tax, I want you to let go of your ankles, stand up, and tell me how good it felt.