Simple fact. Those that feel electrical engine kill devices are needed will always find another reason to have one. Those that don't feel a need for them will not use them.

I have one way to shut off my car. From there only external means are possible. With a full scale aircraft I have two ways, cut the fuel or cut the mags. I have not found a way to make everything I do in life perfectly safe. If I had I would have never had a car or motorcycle accident, or cut myself, or burned myself, or tripped over an item on the ground, or fallen off of a skateboard... You get the point. I won't wear a helmet while skiing, snowboarding, riding a bicycle, or any other activity that did not require one while I was young.