I think the argument goes something like this: if the state lends money to allow more people to educate themselves, then in the future those people will be earn

I think the argument goes something like this: if the state lends money to allow more people to educate themselves, then in the future those people will be earning more money and then be paying higher taxes. Therefore the interest on the loan does not need to pay it of, the increased income to the state from taxes need to pay of the loans.