The point that's being made is-- if there's a certain amount of energy being dissipated in a collision, it's better for things to crumple so that the energy is

The point that's being made is-- if there's a certain amount of energy being dissipated in a collision, it's better for things to crumple so that the energy is dissipated over a long time period and the peak accelerations (which damage occupants) are less. A hypothetical perfectly rigid car that stops instantly in a collision instead of deforming is not safer for the occupants, because suddenly they will be going 40MPH inside a not-moving car.