I find most people misunderstand the national debt because they equate it to personal debt, which it is not. What's the difference? A person has a finite time to accumulate money and at some point, this accumulation stops and it becomes almost 100% consumption. In this scenario, yes, you must pay back your debt in most cases to make your money last.
Now imagine you were going to live and work for 10000 years and every year you were going to make 5% more while the payments on your debt increased at 3%. Why would you need to pay it all back? So long as you can make your payments and because you will always be making money than increasing debt, total debt repayment is unnecessary. You are actually making out even though your debt is increasing every year (your debt is becoming a smaller % of your income). Here GDP is rising faster than the national debt and all is well even though the debt is increasing.
The problem comes when incomes increase by 3% and debt payments increase by 5%. Here debt is rising faster than GDP and that's bad. I'm not arguing our debt accumulation is not out of control...it is...but we don't have to ever pay back the $31T in a one-shot or even in a short period of time and 100 years from now in a healthy economy $31T will look like chump change compared to GDP. The only way we pay back $31T is when it is the interest payment on the much larger total debt that's hopfully part of an even larger GDP.
