It doesn't matter anyway because Bitcoin is not a bank deposit, nor is it a security. Under the law it is generally treated as property. It's still a crime to steal property.

My point is that the fact that it's all numbers in a computer does not make it somehow legal to steal it. What you own is not the abstract number of your private key, but the concrete database entries in a specific blockchain database.

While not relevant, it's also not even true in a pedantic sense that you "can't legally own a number". All digital files are simply long numbers, and copyright assigns ownership of those numbers to people. Also, the DeCSS case established de facto ownership of a private key, making it illegal to copy, so yes you can actually have a kind of ownership even of just a private key under the law. Again, not relevant or necessary for Bitcoin, but interesting.