I sometimes wonder what would happen if Bill Gates and say Warren Buffet spent a ridiculous amound of money on lobbying, in order to drastically change the political landscape.
Think of 'owning' a bitcoin as 'having the ability to spend' this bitcoin.
This ability is guarded by a private key. If this private key is stolen, someone else ALSO has the ability to spend this bitcoin.
Then, if this attacker transfers this bitcoin to another of his own private keys (he 'spends' it), in the blockchain there will be a record, yes. But who owns this new private key is unknown.
What you (or any of us) think about it in moral or ethic terms, is irrelevant.