I don’t see how the conclusion follows. In the example I gave, if the government borrows and spends n pennies in 2017, it will get back n pennies in taxes eventually (if Neil’s argument holds). Assuming 0 interest, that’s enough to repay the n pennies it borrowed; inflation is irrelevant unless the debt is inflation-indexed or something (which I wouldn’t count as 0 interest). Where does the need for “extra tax” come from?