It's science fiction, so wasn't meant to be a full fledged code of conduct.

However, there is a lot of wisdom in those 3 laws. Let's take your proposal that it's merely a machine like any other. And you give it a command to kill your neighbor. Now, you didn't kill your neighbor, the robot did. If you also told the robot to wipe it's memory then there might not be any record that you were the culprit. That's the reason for developing a hard-coded bias in robotic "brains" that embraces something like those 3 laws.

As for spanking, the robot would need to have various parameters - spanking (a swat on the bum) would not cause "harm" but a beating certainly would. In the case of one human looking to kill another, the robot would take any actions needed to prevent such, short of causing harm to anyone, up to an including sacrificing themselves to prevent harm to a human (that's the point of the book/movie).