It isn't debt.
This is what annoys me more than anything about the degree funding debate; it should not be referred to as "debt". It is a retrospective tax, only applicable when the graduate has achieved a certain level of income which they would reasonably expect to have gained only because of the additional education they chose to pursue, and if they don't achieve that income level the taxation is not imposed. Even if they do, the level of additional taxation is negligible when compared to the income.