Actually, like fiat money and gold, a credit system can be laid on top of Bitcoins. One just has to agree to lend them and another has to agree to borrow them and re-pay ... with interest. As highlighted in the article, aggregate credit is then constrained by the performance of the economy/bank assets to the degree that credit is secured by real assets. To the degree they are unsecured (or secured poorly), there is risk in the credit system. Under a "bitcoin standard" aggregate credit would function much like a gold standard and inhibit governments from running fiscal deficits and improve trade balances materially.