If you tax at 100% interest rate, you'll get no tax revenue, because people will have no incentive to work and/or people will move out of the country to avoid taxes.
I don't want to appear to be arguing in favor of 100% taxes, but I think your statement is not correct. Suppose you had a communal society in which the government confiscated (aka taxed) 100% of your income, but then spent all the money it took in providing you (and your fellow citizens) food, clothing, shelter, etc. In that case you would have an incentive to work even at 100% taxation, because if nobody did anything then everyone would starve and/or freeze to death. Of course something like this was tried by the USSR, it required walls to keep people in, and it eventually failed against better economic systems in place elsewhere in the world.
Anyway, with 100% taxation I think you would still get revenue if all the tax revenue was perceived to be being spent wisely on the taxed.