So even if FSD made the very poor decision to slow down or stop right there (and I will point out we have good reason to think this was not FSD, but rather autopilot or human driving), the blame still goes to the rear-ender.
And even if the leading car was non-malicious and merely incompetent, it's your responsibility to not hit anything in front of you. For liability, you worry about what's in front, not what's behind.
The only way you get out of being liable for rear-ending someone is if the leading car maliciously caused you to rear-end them, or if something unpredictable happened that would have made it impossible for you to avoid hitting the other car.
This is literally what happened in this situation. If you have a dashcam and something like this happens, you won't be found at fault.
If you went to court for having rear-ended someone in a similar set of circumstances, that's basically what the judge would tell you. Would that be frustrating to hear? Yes, but it's how it works.
No, the actual research says otherwise
> If this exact same thing had happened 20 years ago, we would all agree that the people to blame are the ones behind.
No, not if someone comes to a sudden stop in a busy lane.
IIRC police has already said that at least some cars involved in the accident did not maintain such a safe distance, and their drivers thus bear their share of responsibility for the crash.