I just finished David Graeber's "Debt", and it really enlightened me on this subject more than anything in that reddit thread. It's one of the most scholarly, informative, provocative books I've read in a very long time. I'm actually reading it a second time through, just to make sure I understand it all.
He is on much shakier territory when he starts to enter into the economists' domain. He's probably correct when he declares that the inefficient pre-money "barter economy" has never actually existed, but then he breaks his arm patting himself on the back to say he's smarter than all the economists who always use this as an example when explaining why we have money.
When it comes time to actually try to explain debt itself, he's really lost. He starts the book by posing a question: how is it that the language of debt got so wound up in the language of morality; by extension, why do we think it's immoral to not pay our debts? He never seems to come around to the obvious answer: that a debt is a promise, a promise of money later in exchange for money now, and that breaking your promises is seen as immoral because it breaks the reciprocity that underlies almost all human interactions. He seems to have a mental image of "debt" as something that a loan shark puts you in so that he can break your legs afterwards, rather than the vast majority of the world's responsible debt arrangements which wind up beneficial to both parties.
Anyway, I'd say Graeber's "Debt: The First 5000 Years" has some interesting bits but a bunch of flaws. And this comment is only this long because I don't have an account on Amazon.