This is what I've now said 3 or so times in various autopilot threads. It has to be an all or nothing thing. Part of responsible engineering is engineering out the many and varied ways that humans can fuck it all up. Look at how UX works in software. Good engineering eliminates users being able to do the wrong thing as much as possible.
You don't design a feature that invites misuse and then use instructions to try to prevent that misuse. That's irresponsible, bad engineering.
The heirachy of hazard control [1] in fact puts administrative controls at the 2nd-to-bottom, just above personal protective equipment. Elimination, substitution and engineering controls all fall above it.
Guards on the trucks to stop cars going under are an engineering control and also perhaps a substituion - you go from decapitation to driving into a wall instead. It's better than no guards and just expecting drivers to be alert - that's administration - but it's worse than elimination which is what you need if you provide a system where the driver is encouraged to be inattentive.
User alertness is a very fucking difficult problem to solve and an extremely unreliable hazard control. Never rely on it, ever. That's what they're doing here and it was only a matter of time that this happened. It's irresponsible engineering.
edit: My source for the above: I work in rail. We battle with driver inattention constantly because like autopilot, you don't steer but you do have to be in control. I could write novels on the battles we've gone through just to keep drivers paying attention.
[1]: https://en.wikipedia.org/wiki/Hierarchy_of_hazard_control