The "argument" is tried against cops when you pass them while driving faster than the speed limit. In the vast majority of cases, if you're going less than 10 over, they will ignore you.
A thing is not legal just because law enforcement lets you get away with it, but I don't think this is a good example. It's silly to have this conversation without at least acknowledging the way driver behavior expands into "grey areas" and gaps in enforcement, and I don't think it's trivially obvious that "self driving" cars should rigidly follow the letter of the law even if that means they'll be the only cars on the road doing so.
A thing is not legal just because law enforcement lets you get away with it, but I don't think this is a good example. It's silly to have this conversation without at least acknowledging the way driver behavior expands into "grey areas" and gaps in enforcement, and I don't think it's trivially obvious that "self driving" cars should rigidly follow the letter of the law even if that means they'll be the only cars on the road doing so.