> where is my opt-out

Don’t tailgate.

That's not a panacea. Realistically, you can easily be rear-ended because you slowed or stopped for a traffic jam caused by something like that Tesla. It is a fantasy that people are in control of every significant danger around them.

Your stopping distance should always allow for the slamming on the brakes of the car in front. If not, you are tailgating by definition.

The scenario is that I am at a standstill because the car in front of me stopped, and am then rear-ended by someone who didn't notice traffic was stopped. Legally, the car behind me is probably responsible, but the car in front of me contributed.

A randomly stopping car is dangerous even to people who aren't tailgating. A human would be charged with dangerous driving for that - which is a felony in my jurisdiction.

Both behaviours aren't great, but the at-fault driver would be at the back. Even though the stopping frequently randomly is likely more dangerous.

Fault isn't necessarily exclusive, and drivers of the front vehicle in a rear end collision may be at (legal) fault. [0]

More importantly for discussion of an automated system shadow braking, however, fault of drivers based on negligence (or more serious mental states, like recklessness) is a separate concept from fault of manufacturers for product defects (which is based on strict liability, not negligence, and therefore bars to liability based on negligence of the injured party due to contributory or modified comparative negligence theories would not generally apply; liability might be barred on a theory of superseding intervening cause, but that would require the intervening cause to be unforseeable—too close freeway following is not so rare as to be an unforseeable intervening cause and thus would not usually limit recovery on a strict liability product defect claim.)

[0] see, e.g., https://www.nolo.com/legal-encyclopedia/is-fault-automatic-r...