The alternative is theft. Thieves are creatures which are incapable of acknowledging and paying their debts. If we believe, as I do, that humans are naturally sharing and caring organisms, much as the bee is a creature of the hive, then thievery is a default behavior, apparently employed by people deficient in what we might call “marketable skills.”
Money makes it possible to engage in thievery surreptitiously. Money also makes it possible for us to keep track of the thievery.