Sorry, but I fail to see the problem here.
It's not that I don't understand the issue, but you've got to approach these situations rationally rather than emotionally. And that paints a picture that is arguably much darker, but can also be seen as optimistic.
Let's start with the obvious: drunk driving is prohibited and highly frowned upon. Why? Not because drunk people actively drive into sidewalks or cause accidents (that happens, of course, but for that you've got to be way more drunk than necessary), but because even small amounts of alcohol lower the reaction time to a position where the reaction time is simply inadequate to properly react to upcoming situations (assuming a normal driving speed).
And guess what: the same happens when your car drives for you. Sure, in theory the driver can instantly spot any mistake the computer driver makes, take over the wheel and stop and/or maneuver the car to avoid collision, driving off the road or whatever it is that the computer attempted to do that wasn't safe. In reality, your mind numbs down when not actively processing the input. It's the same risk that truck drivers face when they're driving the same highway for hours on end: the passivity of monotony can get them into a slow motion trance (they still see the road and can thus 'wake up' whenever something draws near that requires a manoever, but their reaction is seriously diminished). I haven't read much about traffic incidents involving computer driven cars(1), but in the instance where I read about it, it was exactly as I would've predicted: the driver had become so used to the computer driving spotless that he completely failed to react whenever that was needed.
So all in all, the question is wrong. It shouldn't be "why is that guy being dangerous sleeping behind his self-driving car?", but rather "why do self-driving cars still have a wheel?".
The answer to that latter question is rather interesting. It is that Tesla is smart enough to know that they're selling cars to humans, and that there will be humans on the side of the road (the OP video nicely proves that last one, btw)). Whenever we get in an elevator to anything but say two floors up, we pretty much trust the machine with our lives (if it fails, we're dead). But because we're so used to it and the potential danger isn't shown, our guard is down. But meanwhile, we've driven cars manually for many, many years now. Surely we can't blindly trust a machine to drive better than ourselves...right?
The sad truth is that it can. And is busy doing so. But that's thinking rationally. Emotionally, each and every driver claims to have above average driving skill. And I'm sure each and every driver will also put their own skills above the computer, so there is no way that anyone's going to buy a car (yet) without a wheel.
The same goes for bystanders. That little movie could've been part of a horror movie. I won't deny it: that really looks scary to me. And it does so because I've seen people drive cars my entire life and I've driven quite a bit since I'm an adult. But I bet that this sort of thing could become pretty common to the next generation...
(1): which, considering the amount of kilometers traveled, puts them well above human drivers, actually