Interesting point of view.
By “debts” I was instead thinking of the more occasional and private ones (I lent you a book, you paid for my lunch, I take you to work every day, etc.). 

In any case, with this rule even in the financial world the flow of money would happen, you just don't know you have to pay it back and the lender doesn't know he has a credit (not so easy to imagine since transactions are heavily recorded). But things would be built anyway. 
Perhaps the lender, seeing that the other is doing interesting projects, would be spurred to do the same with his finances (and thus consequently lend less).