I honestly don't know what you are trying to say here. Government debt has been discharged before. Look into the number of cities that have declared bankruptcy. (That is, you don't even have to look at failed nation states. Plenty of places in the US have done this.)
That is, no amount of lending is ever risk free. To pretend that you can hedge all risk out of a loan is the problem. It doesn't matter who issues it. It doesn't matter why they issued it.
So, to put the question back to you, why would you feel there is no risk in lending to students to go to college?
It's not about getting the risk to zero. It's about managing it. Right now anyone can take on massive debt to go to college programs they almost certainly will not finish. There's no risk evaluation for individual students, no qualification process that decides to only give loans to those with a history of performance that indicates they will finish. And almost 40% of student loan defaults are people that didn't finish [0].
Whether they finish or not, it surges the demand for education and makes it more expensive for the people that did perform well in high school and achieved a minimum level of personal organization to succeed in an academic environment.
If I loaned out a ton of money to people that couldn't repay it, the system would rightfully tell me that I took on too much risk in lending the money out and that I earned the losses. To that end, the system works as designed and desired. People, by and large, are not capable of putting others in absurd debts that they are unable to get out of.
The way these loans are done, the "risk" is supposedly managed down to zero by some byzantine limits on how much people can take out. This is silly, at face value, as the limits on how much a family can take out are basically non-existent. Yes, we have limits on individuals, but those seem to be little more than token talking points.
That said, reading your post again, feels like we are in agreement?
That is, no amount of lending is ever risk free. To pretend that you can hedge all risk out of a loan is the problem. It doesn't matter who issues it. It doesn't matter why they issued it.
So, to put the question back to you, why would you feel there is no risk in lending to students to go to college?