Some states tax all taxable income at the same rate they have a flat tax rate.?

That is a true statement. Wisconsin, for example, taxes everyone fairly. The rate of tax is the same no matter how much you earn.

The only more fair method of taxation would be very regressive and taxing those that use the system more. A use tax would be the most fair. Taxing those that use any particular service for that use would be very fair. The downside is that most people that are heavy users of the system have the lowest income. That makes this tax impossible.