As companies get bigger, so do banks. What, you think small banks are going to lend to Facebook? Yup, you're a real financial expert you. Never mind that mortgage backed securities are the way the US economy (and most advanced economies) have funded home purchasing for two decades now, and still largely do. Never mind that "accepting deposits" isn't actually how banks make money. Never mind that "lending money" isn't nearly as straightforward as you might think. Never mind that banks actually have to do something with the money that they hold. Never mind that banks do actually need to hedge exposures so that loans made to lenders don't crush them. Never mind all that - you don't need to know any of it. You just like the analogy, that's all that matters. Do you help run Occupy WallStreet?