It’s relatively easy to make a car exterior that won’t crumple in an accident, the reason cars don’t have that is that the inelastic deformation of the car structure absorbs quite a lot of energy during an impact, which would otherwise be transferred to the vehicle in form of kinetic energy. You might say a little energy difference is not important but for a passenger or a pedestrian / cyclist hit by the car it can be the difference between suffering light bruises and dying from the impact. When I saw Tesla’s design with the ultra hard steel and sharp edges I immediately thought this thing is a large danger to other people on the street, especially cyclists and pedestrians.