No point in having it take zero damage if it transfers the energy to your squishy body.
Having been in the exact result of a 1963 Plymouth hitting a 1982 Ford square in the middle of the back bumper at 30mph, my squishiness walked away from it just fine, as did the Plymouth's roughly equally squishy driver.
I'm sure things would have been uglier had her car not had 3 point belts, which I assume were a retrofit. Proper restraints would do a lot more for safety than crumple zones, but people who can't resist digging in the back floorboard while cruising down the freeway don't like 5 point harnesses, and certainly wouldn't put up with non-auto-tensioning ones that keep you right there in the damn seat in front of the damn steering wheel paying attention to your damn driving so you won't need to test the crashworthiness.
IMO, they also need to add a section to the driving test where the examiner asks a series of questions while going down the road. If you can't listen and respond without staring at the examiner, you fail.
(ETA: then have a second examiner call your cell phone with more questions. If you put it on speaker, then continue holding it up in front of your face, the one in the car with you activates his ejection seat and the 5-second delay on the car's self destruct device.)
