Just to set a few things straight about this subject. Most people plead for ignorance in this matter, the others just parrot the prevailing narrative and ridicule everybody who questions it, without being willing or capable at all of thinking about it on their own.
Public debts are supposed to be repaid at some time in the future. Their ever rising amount makes this rather unlikely, but okay. At the same time governments retain the monopoly of creating money, this means, that they could always just print any amount of money they want to, at will. Usually money is supposed to be backed by bonds, although this is not at all necessary, because the government’s currency is legal tender and taxes are collected in it, so it will always retain its value, if backed or not. If money is created only in exchange for bonds, this raises the question if the total amount of bonds has to increase forever and what to do in a shrinking economy. Deflation is harmful to the economy, because it leads to money hoarding which a creates positive feedback: The more the value of money increases, the more people will want to withhold instead of spending it, thus further reinforcing economic recession.
But back to public debt. Why don’t governments just print the money the need instead of borrowing it? Because that could cause inflation, as the potential lenders would still keep their money for potential spending. However, every government has the option of just taxing people instead of printing money. Presumably taxing is politically less popular. People don’t care about public debts as long as 1) the taxes are not going to raised and 2) there is no undue inflation. So just borrowing money does the trick to increase public expenditure while satisfying both conditions 1) and 2).
However, there is a catch: The government has to pay interests on its debt. The higher the public debt is, the higher the interest to paid, from tax revenues or from even more debts, because people want low taxation and high public expenditure at the same time and don’t care about the future.
Therefore eventually resolving the over-indebtedness by printing money or by not paying interests and/or repaying debts can’t be avoided. Now sane people would oppose making debts and public expenditures exceeding tax revenues in the first place, but then sanity is rare among human beings.
