If every country bans bitcoin and they control the internet it would be no matter time for bitcoin to fall down to zero. It is really easy if they work together.
So in short it is possible to destroy bitcoin and his value.
i think there is no such way to destroy bitcoin if it was possible then those countries who have banned bitcoin in their country will have destroyed bitcoin but its not possible.bitcoin is very safe and no one can affect the rate of bitcoin and it is more expected that bitcoin will become the international currency in the future.