No. Invalid comparison. If you legitimately discover a cryptocurrency wallet private key by sheet lucky, and such cryptocurrency has no backing = is based in pure thin air, such as the case of Bitcoin, and there are public nodes which doesn't require you to abide by contracts that would forbid you to do so (which is supposedly all nodes), you're good to use that as you wish and it won't be a crime.
It's unethical to steal something tangible. Bitcoin has no tangibility whatsoever. You can't steal it.
Property is legally defined as 'Not only money and other tangible things of value, but also includes any intangible right considered as a source or element of income or wealth.'
That includes protectable ideas, digital files, financial instruments (like stocks and bonds, loans and credits), computer graphics, certain arrangements of words and quite a bit more.
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What does tangibility mean to you? That allows you steal the examples in the second paragraph without legal reprecussions nor ethical dilemmas?