Here is how this would work. It is a debt tax. While it will be to discourage people from taking loans they cannot afford, it is actually based on the amount they owe.
When someone takes a loan and goes into debt, until it is paid off they have to pay taxes on the amount of debt that they owe minus any money they have in non movable funds such as savings accounts and 401ks.
Just like the income taxes are now, they would have to pay by tax brackets. The more they go into debt, the higher the taxes are that they have to pay. This bracketing will discourage them from borrowing even more money that they don't have and can't ever pay back. Like people who don't pay income taxes, a select few of the individuals who don't pay their debt taxes will be placed in jail. Since this is to discourage people from taking irresponsible loans, Ex post facto law will apply and someone has to take a new loan out before the tax applies to them. This also wouldn't apply to people who go into debt for emergencies such as hospitalizations.