That's true to some extent, but there is the free rider problem. That's why taxes are mandatory. Suppose that I would be willing to pay 30% of my nominal income in exchange for a functioning government similiar to the current government.
Under a strictly voluntary system, would I pay the 30%? Of course not, because whether or not I pay the 30% has no bearing on whether there is a functioning government. I, and millions of others, even if we were all willing to pay and would all be better off, would end up not paying, and we would all be worse off.
This is why, some people may be willing to pay more taxes, but it is always contingent on others paying.
If you honestly believe that your taxes are too low and state so publicly, the free rider "problem" shouldn't be an issue. Perhaps the "others" don't think their taxes are too low, and ought not to be forced to pay more just because one of their peers wrongly thinks they are not paying enough.
If I were king for a day, I'd tax Congressional pay at the highest rate, subject to the same nonsensical phaseouts and limitations as those in the top group. I'd also tax political donations at the highest corporate rate, subjecting them to the same nonsensical deduction limitations as companies in the real world.