Because it is generally proven to save lifes. You'll never hear of "thanks for the auto-brake system no one got injured and everything was boring as usual" but it happened a lot (also to me in first person).
I don't like Musk but in general its a good thing to push self driving cars IMO. I drive 2 hours per day and the amount of time where I see retarded people doing retarded stuff at the wheel is crazy.