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.
Copyright doesn't cover the computer reference machine code number, it covers actual intellectual content.
Just like it is not settled whether Ethereum or Bitcoin is a security- thoughts on this can and will change, new regulators get elected... neither is settled whether you can actually say that you own a number.
The community has misplaced confidence imo.
Saying the law could change is literally always true, it means nothing. Will it change? You could make an argument for Ethereum, and I tend to agree that the community is overconfident about the regulations around Ethereum and other coins. However for Bitcoin specifically the SEC has been very clear and consistent in stating that it is not and has never been a security. Their justifications are sound. So no, it almost certainly won't change for Bitcoin.
Copyright covers the specific number in addition to the general intellectual content of the number. You could say it covers a family of related numbers. That's stronger than just covering a single number.
Bank deposits are financial assets- which gets its value from a contractual right or ownership claim.
When you deposit money in a bank, they lend that money out, they make a return, and in a sane world you would receive interest on that money.
Using this definition of a financial asset, I don't think bitcoin qualifies, it is more of an intangible. It might be a financial asset only if it is held at a custodian.
Congress and the courts decide what a security is, not the SEC. The SEC is the enforcement agency from what I can tell.
It's also unlikely that Congress would change the existing definition to apply to Bitcoin. It's much more likely that they would pass specific regulations for Bitcoin and cryptocurrency.