On page 53 of the "Adventures in Automotive Network and Control Units" paper there's a photo of what happened to the researchers garage after a command to run diagnostics on the brakes left the vehicle unable to stop even at slow speeds http://illmatics.com/car_hacking.pdf
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Poking around an unknown device's network and sending arbitrary commands to see how it responds could certainly very well damage something.
So could poking around the physical components of the car.
But people are well within the right to do so.
On page 53 of the "Adventures in Automotive Network and Control Units" paper there's a photo of what happened to the researchers garage after a command to run diagnostics on the brakes left the vehicle unable to stop even at slow speeds http://illmatics.com/car_hacking.pdf