No. You're not stealing from anyone. It's decentralized and bits have no owner.
If you say 'hey, here is my Bitcoin transaction' and others accept, and you just had luck to find a valid address, it is not the same as stealing. Bitcoin has no value.
That isn't true, although you might like the philosophical debate around that, a judge is still going to make you pay the person back and/or give you a prison sentence if it's proven that you are the original owner of the keys. He's going to laugh at your digital philosophy as he slams his hammer down upon judgement.
