If someone hacks into your computer and steals bitcoins, you report them to the computer crimes division of the police. It is not the job of the currency itself to enforce fairness. If someone steals $100 from me, it's not the Federal Reserve that gets involved.
No more than I expect them to return stolen property. If I had a large amount of bitcoins, I'd probably want to insure them, or at least keep the private key in a secure location, such as in a security deposit box.
The police act as a deterrent, and make it more difficult to offload stolen bitcoins without being caught.
