Yannis, just wanted to comment on a number of your statements above that are demonstrably incorrect and answer a question or two that you had, where the answer is known.
First "effective tax rates" are not all all "murky". They are known with great accuracy once you have defined "effective tax rate" and the cohort they apply too.
Economists agree on the definition of a progressive tax. It is a tax where the greater one's taxable income the greater the effective tax rate. For a cohort consisting of the top 1% in taxable income the effective tax rate is 15%. It is not at all difficult to define a middle class cohort for which the effective tax rate is a little > 15%. Thus the tax as it relates to these respective cohorts is regressive, not progressive. It is not anything that can be argued about. Facts are facts whether we like them or not.
I don't know what you mean by "regular rates" as the effective tax rate is "regular" by definition. I think what you were asking is "why is the effective rate for the top 1% lower than for a cohort with smaller income?" If that is what you wanted to know, then you have answered your own question; it's because for most in the top 1% much of their income, for some all of it, is unearned income which is taxed at a lower rate by the IRS than is earned income.
Incidentally, I applaud your "reluctance to belittle those most talented, dedicated and successful among us who are making the whole economy work. " Good for you I say! Please recognize that many in the top 1% are "rent seekers" to use economist speak. There is very little productivity associated with rent seeking. You'll find those that you are properly reluctant to belittle mainly in the middle and lower income classes.
