And then there's the time to actually make your movements. Getting your foot onto the brake pedal and pushing on it takes appreciable time, both for the foot to make the movement and for the nerve impulses to get there to make it move.

I recall from looking into this stuff a bit that a good reaction time from "oh shit" to "brakes are applied" is around 750ms. Accounting for people who aren't fully on top of their game (distracted, tired, injured, old, etc.), road designers assume more like 1.5-2s delay for applying brakes. And even that will be optimistic in some cases, as many car crashes demonstrate.

There's that, but also the realization that you need to brake "as hard as possible"-- we're not trained to do that often so there's additional delay before that happens.

Hence why he said "ideal".

And my point is that talking about the ideal human response time is absurd in the context of driving.

Why? It provides an lower boundary on the human response time. It's significant because the ideal response already represents _at least a whole car length_ of travel distance. We don't even need to delve into what a realistic response time is: it's already so bad that we should be looking at alternatives like our machine-overlord-self-driving-cars.