This is simply not true on its face.
Unlike the thought expirement you’re running in your head, the real world does not have the luxury of avoiding the possibilities of sudden mechanical failure, a soccer ball being kicked into the road, or unsecured debris falling out of the bed of a truck. These are privately owned and maintained vehicles after all, under many more engineering constraints and usage pressures than just achieving maximum reliablilty in all conditions.
These things require some degree of margin for error. In general, any car should be able to fully stop before entering the space currently occupied by the car in front of it in order to account for unexpected disturbances. However, as car speeds increase, so do the tolerances required to maintain that safe margin, exponentially in fact.
Removing the human from the driver seat doesn’t mean we get to start running bumper to bumper at 70mph; at best it means that cars can get away with slightly smaller follow distances than humans need to account for their comparably slow reaction times.
If you instead believe that we should exert enough control over self driving cars such that we could actually realistically prevent catastrophe while running high speed bumper to bumper traffic, then I have great news for you! We already have that, and it’s called a train.
I don’t refute that. I agree that far too many humans are far too comfortable with unsafe following distances.That’s not the claim you made though:
And as I said, it’s just simply not true. Congestion happens because car traffic does not scale or recover from disturbances efficiently. Human behavior exacerbates this, sure, but cars are just fundamentally bad at moving people when a road is at capacity. Chalking traffic it up to “human error” alone misses the forest for the trees.