The money a government gives to citizens must come from somewhere. They could liquidate assets owned by the government, borrow it from another government, take it from entities who are subject to the government's authority (taxes), or - what I assume you're getting at - just make more of it.
That last one isn't as simple as it sounds because it doesn't increase the cumulative value of the currency. Printing dollars is like dividing a pizza into more and more slices. It doesn't increase the amount of pizza. Inflation is a very real problem that has annihilated economies.
In any case, value fiat money is not a product of rarity, it is a statement of the value of future tax receipts. Money encodes/is an exchange marker for work done or promises of work to be done.
The notion that we can't do this, is the one i have problems with because its absurd.