That's all well and good, but the simple question is: Are we morally obligated to pay back money we borrowed from a bank? I hear a lot of people using smoke and mirrors to dodge the issue. The answer is simple; yes we are unless the contract is illegal, and that's up to a court to decide.
So why is it up to a court to decide whether or not the contract is illegal, but not up to a court to decide whether or not the defaulter has truly defaulted? The bank is trying to impose God's standards on people, while using man's standards to allow it's illegal activities.
Man's standards allows the bank to commit fraud and to steal (commit usury). Man's standards also allow for a person to default or go bankrupt on a debt they can't repay.
God's standards do not allow banks to commit fraud or to steal (i.e. commit usury or charge interest on loans). God's standards also require men to honour their word with respect to debt.
The bank is using man's standards for itself (by it's acceptance of fraud and stealing to make money), but then demanding that its debtors comply with God's standards to pay back the money defaulted on. In short, they're trying to have their cake and eat it too. Banks have done this for too long, and this is why they are all going bankrupt. Dishonestly profiting from dishonest money.
So if it's left to a court to decide whether a contract is illegal, it's also up to the same court to make the defaulter pay back his debt.