This particularly protest is elegant because it's effective exactly to the extent that self-driving cars are not adaptable—it highlights the brittleness of the system by getting a substantial effect from a small nudge.
I think it highlights how the system is tuned to safety over all other concerns. If there had been cones put on vehicles being driven by actual humans, you'd probably have had a few bad injuries or deaths.
To be able to focus on something above all else, you first need to be able to unequivocally define what "it" is.
What is safety? It's not always the same thing, which is why the simplistic models of these cars fail to do the right thing in some edge cases where a human would know what to do.
Generally it seems they simply slow down and stop when confused. Which unarguably is very often the safest thing to do.
But then there are the examples where the car stops, blocking emergency vehicles. Clearly not the safe thing to do. Human drivers sometimes do things like drive up into the sidewalk to clear way for an ambulance in a tight spot. Driving onto a sidewalk is nearly always the worst possible thing, but sometimes the right thing to do. It's easy for human drivers to make this judgment.