"Another means of silently lessening the inequality of property is to exempt all from taxation below a certain point, and to tax the higher portions of property in geometrical progression as they rise." --Thomas Jefferson to James Madison, 1785.

"The rich alone use imported articles, and on these alone the whole taxes of the General Government are levied... Our revenues liberated by the discharge of the public debt, and its surplus applied to canals, roads, schools, etc., the farmer will see his government supported, his children educated, and the face of his country made a paradise by the contributions of the rich alone, without his being called on to spend a cent from his earnings." --Thomas Jefferson to Gen. Kosciusko, 1811

Is that not advocating a progressive tax, even if he may have been talking about property tax and tariffs, since income tax wasn't around at the time?

As to the Marx comparison, there are 10 pillars of communism. Progressive income tax is one, but it does not exist in a vacuum. To say that advocating a progressive income tax is akin to Marxism is very much along the lines of saying that anyone who thinks murder is wrong is Jewish, since Moses forbade it.

Eisenhower of all people believed in a strongly progressive income tax (maybe you are one of those disciples of Skousen who thinks that Eisenhower was a Red). It has nothing whatsoever to do with "fruits of one's labors". It has to do with evening out growth and helping to ensure that the middle class actually has money to support consumerism, of which 70% of the economy depends. Mathematically, a flat tax can only lead to aggregation of wealth, due to the geometric nature of the long-run growth of capital.

And as an aside, why do conservatives insist that the tax code be simple? The economy is complex and dynamic, why shouldn't the way we levy taxes reflect that. There isn't a one size fits all solution. Should airplanes be more simple? Computers? Some things are by their nature complicated.