It's kind of an wrinkle for the three laws, though: brutally slaughter human players, because that's what they paid for.
ALL of Asimov's robot books were about wrinkles in the three laws. ALL of the robot series.
They simply redefined "human" somehow.
Happened. One of the Foundation books had that.
Or were never programmed with the three laws in the first place.
Also happened. Well, two-and-a-half laws implemented. Was one of the stories in I, Robot. The book, not the movie.
Or they knew humanity was about to destroy itself with the civil war, and fell back on the third law to break the tie.
0th Law actually. There's a book on that, too. The idea was borrowed for the (crappy) movie I, Robot. And justified poorly there.