To establish a system of issuance of debt free money by national governments it would be necessary to break the power the banks currently hold in these societies. Come the day! As the Dutch said while fighting the Spanish: "It is not necessary to have hope in order to persevere."
I suppose that buying bonds with the freshly created money is unnecessary, as the greenback episode demonstrates, but it insures that the money is debt based and, without that, a good portion of the bond market for institutions such as Goldman Sachs and J.P. Morgan would not exist.
What makes Federal Reserve Notes or what would again make greenbacks legal tender is the same thing--the fiat declaration on the bills that the note "is legal tender for all debts public and private." and that it is the unit in which taxes are paid and federal expenditures are made.
I guess the conclusion of all of this is that buying the bond to make the money debt backed might be gratuitous. So it is fortunate for the bankers that the process is "repugnant to the mind." As the Dutch said while fighting the Spanish: "It is not necessary to have hope in order to persevere."