If people borrow money, shouldn't they have to pay it back?

Among the several arguments about how to solve the current debt crisis, one is that people who borrow money should be given some special consideration, even forgiveness, when it comes to paying it back. Which means that the people who loaned the money have to suck it up and figure out what to do next. Which means that a a pretty basic moral principle, which is that if you borrow something you are obligated to repay it, is suddenly up for arbitrary grabs.
So does that mean that there really is no obligation to pay back debt? One should only have to do it if it is convenient? Otherwise, one can simply forget about it and let the lender figure out how to pay back their own debts as if it never happened.