This is not about the moral act of stealing, is about how laws are applied. And laws, including the ones for stealing, take in consideration the prejudice, so I don't think that in any country you would end up in jail for taking a piece of blank paper.
But if you want it we can make a different scenario where one just scans/take a picture of the QR code from the wallet. And the wallet is in a public space, so you would not mention invasion of privacy or smth.
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If you aren't the sole controller of your private keys, you don't have any bitcoins.
Yes, and if you are not in charge of your cash you don't own it, but still there are laws which protect me from people that try to steal my cash.