Not Tax, Monopoly
A patent is the grant of a limited time, legally sanctioned monopoly right to make, use and sell the patented invention. Patents are issued to encourage inventors to invent and to commercialize their inventions by allowing them access to the market at the full price the market will bear rather than at a price tied, by competition, to the cost of production.
If you want to use something I have invented, you can merry well pay me what it's worth or go do it some other way.