The Buffett rule is designed close the loophole. That loophole lets people making millions from finance pay a tax rate under 30%. But it makes a already uneven tax code more discontinuous. This only targets a very small number of people in a very specific situation. But I think it would make sense in most cases.
Personally, I think something like a flat tax on every dollar earned above the poverty line, no matter the source (ie: wages, capital gain, or profits of a corporation as a “person”) should be taxed at the same rate for everyone. With few or no deductions, and the rate should be high enough to balance the federal budget. This does several things and I will write more on it in a future post. Flat taxes are or have been advocated by many people including: Steve Forbes, Herman Cain, Rick Perry, Jon Huntsman, Daniel Mitchell and Newt Gingrich.