I've not read this thread in full, but...
Braking on the motorway is the work of the devil. OK maybe not the devil, but a bad thing indeed. It interupts the flow of the traffic as a other drivers react immediately whether required or not - either by braking or changing lanes, which then prompts another driver and so it continues.
The danger is probably some way behind the tailgater and brake-dabber, as the concertina effect increases in intensity.
Not sure if it was a dab of brakes due to tailgating or some other reason but I observed exactly this on the M1 last week. On a downhill straight stretch I saw brake lights flash on and off way into the distance which propigated back towards me along with the odd lane change. The driver in front almost had to do an emergency stop.
Of course if the gap between cars is a safe distance then there is no need to react immediately but the sad reality is that there is seldom a safe gap.