Depends on the size of the society. If you think about it from scratch, you only need lending once society grows to about a certain threshold where you're essentially dealing with unknown people. Interest is a compensation for the risk you take, combined with the loss of investable capital during the loan period. It's quite different from helping your friend or relative build a house, along with a dozen other members of your society, with the social agreement that that friend will help you out when you are in need. Most of our societal issues I think stem from stepping above the size of our social circles.