Mark Thoma writes, on progressive taxation:
Economist's View: Progressive Taxation as a Political Shield for Globalization: First, when there is change such that makes one group better off at the expense of another as has happened recently with globalization, and when redistribution can leave everyone better off, then redistribution is justified.
Second, I think everyone should have equal opportunity to be a CEO or a hedge fund manager, or whatever they want to be. However, the playing field is far from level and there is a lot more we could do on this side of the equation. Not everyone will be a CEO of course, or achieve their dream job whatever it might be, but everyone should have an equal chance to be one of the winners. In the meantime, until more has been done to level the playing field, progressive taxation is a means of making up for inequality in opportunity.
Third, for me at least, progressive taxation is justified by the equal marginal sacrifice principle (the last dollar paid should cause the same amount of disutility for everyone). Thus, even if opportunity is equal, and even if there were no winners and losers to worry about, justification for progressive taxation would remain. I think a more progressive tax structure than we currently have is needed to equalize the disutility of paying taxes.
We could list "preventing a political backlash" as a fourth reason for redistribution. But I'm not sure we need to invoke the political economy argument. If we use progressive taxation in accordance with the three principles above, then income will be more equally distributed and a backlash against globalization is less likely to occur.