Because a lot of this is transient signals that are crap? One of our robots back in '06 would panic stop every 30 seconds or so whenever there was a dust cloud

Because a lot of this is transient signals that are crap? One of our robots back in '06 would panic stop every 30 seconds or so whenever there was a dust cloud (this was an army off road formation project, so dust was a fact of life for all the followers) because occasionally there would be enough random scatter returns from the dust to convince the MMWR that there was a wall in front of it. Panic stopping from highway speeds every time your MMWR detected a flyer floating in the breeze near some dust seems like it would be pretty dangerous- especially for the cars behind you that are also traveling at highway speeds. And LADAR doesn't have the range to be useful at highway speeds (from memory, the ratio of range to safe braking distances means you can't get above 25-30kmh with LADAR being useful for you). As for whether having shared autonomy at highway speeds is a good idea, that's a really good question that I hope Tesla is asking itself right now. But if you are trying to do that, cameras pretty much have to be your primary source of truth.