I'm currently reading the Harry Potter book series aloud to our children (mostly to Kid 3). We are about 10% into the fourth book.
Last night at dinner I asked, "Why are the Weasleys poor if they can just make things appear ex nihilo?"
First, there are a few times in the books so far when a wizard waves his wand and creates things from nothing. The most recent example I read was from the middle of Chapter 5 of Goblet of Fire (sorry, this Kindle version doesn't have page numbers), when "Bill reattached the table leg and conjured tablecloths from nowhere." It seems to me that someone conjured a stool once when he wanted to sit down; I remember that one because the kids had a laugh about conjuring stool.
So, granted that wizards can magically make things, why are some wizards poor?
My family's first answer was that you can't conjure money. But money only has instrumental utility. This raises an even bigger question for the wizarding world: what are they doing fooling around with money when they can just create any item they might want to buy? I guess that might be too strong; you can't "create" someone else's willingness to cooperate, but that person will sell it for the promise of future goods and services, which is what money represents. So okay, wizards, keep your money, but why does Ron Weasley have robes that are too short, and why does Molly Weasley have to knit terrible sweaters? Just wave your wand, Molly, and make as nice of a robe as Draco Malfoy's parents buy for him.
My family's next answer was that you can't conjure food. I mentioned that Dumbledore conjures up food for the end-of-year feasts, but my family adamantly denied that. "It was prepared in the kitchens by the house elves! He just magically brought it to the table!" Fine, you can't conjure food. Then conjure everything else and save your money for buying food. Then the Weasleys would be malnourished, but at least they'd be well-dressed.
My family's next answer was that "conjuring" didn't "create" so much as "summon." When a wizard waves his wand, he's not making a stool, for instance, but he's bring it from somewhere else. Wizards are subject to the conservation of matter. I said, "So any time a wizard conjures something, he's stolen it from someone else? So all wizards are thieves. Muggles are right to distrust wizards."
No, they're not stealing. They're moving around their own stuff, my family claimed. My wife said, "When Hermione has that Mary Poppins bag, she still had to pack it first. It doesn't just give her stuff." (No, but the Room of Requirement does.)
Then one of the kids said, "Harry couldn't just conjure a Firebolt, he had to buy one." I asked, "So wizards are bound to obey intellectual property laws? Are wizards not libertarian?"
I don't feel I got a satisfactory answer. I think J.K. Rowling wanted the "wow" factor that comes from making stuff out of nothing, but needed the wizarding world to be familiar enough that the characters had similar problems and concerns to those of her readers. She needed poor wizards so the rich wizards could act reprehensibly. So much of the wizarding world is just complacent in the face of side effects and negative outcomes. Every Flavour Beans don't obey the basic axioms of utility. Bertie Botts would be driven out of business when his conniving brother started selling "just the good ones."
Posts like these are how old men get to be called "cranks." But I think it's important for the defining children's literature of a generation to not get its economics so wrong. Why are wizards Luddites? Why use parchment, when paper is superior? (How do we know paper is superior? Because when paper was invented, it displaced parchment!) I feel like all of Hogwarts is a path-dependence story that answers the question, "But how'd we get on that path?" with some version of "turtles all the way down." Was Godric Gryffindor's vellum shop shut down by the predatory practices of Tesco Paper Manufacturing Concern, Ltd.?