If every driver were drunk at all times, roads would be designed with that in mind. It's much harder to dangerous things in a car with better designed roads
The point is that the design of the vehicle, or anything, needs to be as good as possible regardless of anything else, and there is no overriding excuse not to.
It's not like the poorly designed controls are necessary for some other even more important reason.
If both roads and drivers were all excellent, the vehicle still needs to be as excellent as possible. If all other factors are so good that only 10 people die each year from car accidents, there is still no excuse for making vehicles less safe and make that become 20.
Alcohol, lack of alcohol, good roads, bad roads, speed limits, none of that matters.
If every single driver were legally drunk at all times, poorly designed vehicles will still result in more and worse accidents then well-designed.