Who's to say that you'll feel the same way after an injury as before one? What a nightmare that must be, to realize after the fact that you do want to live after all, then be euthanized for your previous error!
An important point! Many people are terrified of disability, and think they'd rather be dead, in theory. They often find they'd rather be alive, when faced with the situation in reality.
It's not, I believe, that the fear of death is so overwhelming that any life is preferable, but rather that the fear of disability has been tremendously exaggerated.
Our culture holds that a "meaningful life" is one that is productive, and that "dignity" means autonomy. The disabled and those who work with them remind us that these ideas are false.