A couple of interesting responses to my question before the weekend about copyright and theft.
First, Sergio Muñoz Sarmiento has an entertaining post that, I think, boils down to the claim that "property law and intellectual property law [aren't] synonymous," which was precisely the point of my hypothetical (or one of them). He says, in considering a case of possible copyright infringement, "we use intellectual property law (with the term intellectual being key, meaning that it is, unlike real property, intangible), and thus, we apply copyright’s 'fair use' schema and its four non-exclusive factors." That's quite right, and there is no analogous schema when it comes to personal property: we don't ask whether taking someone's wallet was educational, or a parody, etc.
Michael Rushton responds too, focusing on the incentives to the appropriator: "Here's the policy problem: if I could take someone's wallet and they would still have their wallet, then I could quit my day job. Why bother going to work to earn money to put in my wallet if I can just spend my day as a pick-pocket, and do so with a clear conscience, since my marks haven't really lost anything - they still have their wallets (and now I do too)." But he adds that "it is not an all-or-nothing problem, since some appropriation, some fair use, increases creators' abilities to make new and interesting work. The optimal fair use provisions establish a balance between maintaining incentives for new work and for the ability to build upon existing work."
I think both Sergio and Michael are exactly right to stress the idea that what's required in the copyright context is a balancing of interests. So it doesn't seem helpful to me to just scream "BUT THAT'S MY WALLET." The question we're trying to answer in the copyright context is when is it okay for me to take your wallet, and when it's not.
UPDATE: More from Colberg.