Plato: “When there is an income tax, the just man will pay more and the unjust less on the same amount of income.”
Adam Smith in the section “Taxes upon the Wages of Labour” of The Wealth of Nations: “Absurd and destructive as such taxes are, however, they take place in many countries.”
Albert Einstein: “The hardest thing in the world to understand is the income tax.”
Will Rogers: “Income tax has made more liars out of the American people than golf.”
Please post more quotes in the comments.