some wealthy entrepreneur decided to drop a total of 1 billion business cards, having a blank bitcoin address and its private key on each side of them, from air to ten major cities of usa? Would the common folks be interested in using these cards as regular money? Would this act be permitted by law?
You didn't mention, that there were any Bitcoins in these "blank bitcoin adresses", so I guess it would be easier to create your own private key, instead of using a compromised one from a random card that you found on the street.
If there actually were Bitcoin in it, I would instantly send them to a wallet, that only I am controlling.