The question is not a flat tax vs the complicated mess that we have now. The right protest is to eliminate all the unnecessary spending so that we need no money from the income tax.
If the Federal government obeyed the tenth amendment, then a long list of illegal "services" would be eliminated and roughly 2/3 of the budget would go away. What is left can be paid for with various existing excise taxes and, maybe in war time, a small head tax collected by the states for the Feds in accordance to the original plan of the constitution.
Sorry, missed this one. The idea would be that the Feds could NEVER take more than 10% from each one of us. Never, never, never. Not even in emergencies or wartime. Unless it was voluntary. They could set up a fund to which each of us could donate to any war effort. We're going to have to pay for it one way or the other anyway.