And as you point out, it is a legal contract. Which, by implication, makes it subordinate to the laws of the land. Those laws include laws on debt repayment. These contracts will not override the laws.
This means there is implicit bankruptcy protection (now changed by a change in the laws) as well as collection protection and the like. It is, as has been pointed out, an unsecured loan.
Drew Garrett
"Vote for me, I'll set you free".
An unsecured debt is still a debt. The money is owed. The person who doesn't pay his freely taken responsibilities is a thief.