Hmm, I think that is actually a very interesting question. In general, private keys are not scarce. However, those which unlock my funds are, as are Bitcoins themselves. Admittedly, by merely copying my wallet, you are not denying me the use of my funds, but as soon as you actually send funds from it you are. Additionally, it is likely that in order to copy my wallet, you made use of my physical property (computer) without consent.