Public debt is, in fact, never truly repaid; it is only replaced by other debt.
However, beyond certain limits, debt does lead to many difficulties, including inflation. Therefore, in effect, it is paid back by everyone, but for the poorest people, it becomes a severe hardship.
The resulting political problem is this: What are these limits? For example, in Germany, they are considered to be stricter, while in Italy, they are less so.