Road throughput is inversely proportional to following distance, so if everyone doubles their following distance to account for / avoid spurious automatic emergency braking, then we’d need to double the number of lanes to keep road capacity constant, which would lead to more lane changes, and therefore accidents.

If, instead, we kept the roads the same, then congestion would increase, and with it, accidents.

There is a reason that random unexpected emergency braking is a favorite tactic for people attempting to force accidents in order to commit insurance fraud: It’s too expensive for everyone to change their habits in order to guard against it.