It seems ridiculous that the federal government should require such revenue. It really has the legitimate power to do very little, and much of it, they could fund by assessing fees for the users.
For example, coining money and operating post offices. These could be funded by those who choose to use these services.
Other than that, we have the army and navy. Since we are not in a state of war, we don't need a standing army. Which leaves the navy. So, our federal taxes need to provide for a navy to defend our shores. I can't see how that would be any more than 2-5% of income.