(I don't know enough about the CFAA to know whether this is true so I'll assume it is.)

To continue the garage door analogy, you wouldn't walk up to any random garage door and try code 12345 to help protect the owner's stuff, would you?

To stick with this analogy: I think a white hat equivalent would be more like driving down the street with a garage door remote set to a default code and then notifying anyone whose door opens in response that they should change their code. I don't think that should be illegal.