The category of "illegitimate national debt" is huge. Many peoples live in countries whose leaders chained them to debts that "must" be repaid by the people, who actually did NOT have any say over or even awareness of the decision to encumber the nation with un-repayable debt.
It sounds as though you are asserting that ALL "national debts" are legitimately to be enforced to be paid by the peoples of those nations. Can you think of any historical examples that aren't?
You might acquiesce to an assertion that the people of Uganda are not compelled to repay all the debts that Idi Amin ran up. If not i guess we have nothing to discuss. But if so, do you recognize a wider category of "national debt" that could legitimately be repudiated by the peoples of those nations?
If so, where lies the line of demarcation?
Historically, which massive debts have been duly paid? Which debts have not? Surely you recognize that many such "debts" have never been paid? And the world has not unduly suffered?
Why is it that your tendency is to react in support of monstrous financial elites, against the interests of the common people?