No use of your body is a pretty desperate situation. Before the procedure he had to yell for his parents that he wanted to use the computer, they’d come sit him upright and put a joystick in his mouth, leaving him unable to speak. And he was often very uncomfortable in that position, so he couldn’t do it long. Now, he can use the computer fully laying down, without anyone’s help. The next logical step would be to have some robotic helper arms.
Anyway he can’t shoot himself. He can’t hold a gun or anything else. There’s little reason for this to be about Musk at all other than money. This is the culmination of decades of research from many medical professionals. It’s about a lot more than one person.