All debt even government debt must be repaid at some point.

Why? How long has your public utility been in debt? Do you think it will ever not be in debt? Do you think your banker will ever not be in debt? Only things that die need to repay their (unsecured) debts.

Modern monetary theory proponents will say that as long as the debt issued is denominated in your home currency, you can always print the money to pay back the debt (or print the money to buy the bonds in the first place).

No, not "always." MMT makes inflation the bogey. MMT says that the debt is a problem if servicing it will cause unacceptable levels of inflation. That is where our attention should be focused.