As I understand it from previouse posts hard breaking is only considered to happen when the ABS operates and is why some believe the flashing lights should only come on then. But let's face it hard breaking doesn't only occur when the ABS operates, I've break hard on many occasions without it cutting in.
With regard to positioning the flashing lights to avoid dazzling. Can't see this point, flashing the 3rd brake light doesn't increase the brightness it's just the same, maybe less because it's going on/off and no one complains about the Z 3rd brake light brightness at the moment.
As I've mentioned above, following activation, the light doesn't flash again until a programmable time has elapsed so driving in traffic shouldn't be to much of a problem for other drivers.
I'm still not convinced by the against reasoning but I am concerned about the legal aspect.