The way Elon Musk tells it, they put it into production once it was safer per mile than human drivers. Which seems like a legitimate point.
You use something when it's better than what you would have to use in the alternative, not when it's 100% perfect with no possibility of ever making a mistake under any circumstances. Which is probably not even actually possible to do.
The problem is if human drivers kill more than 30,000 people in a year, it's not news, because it's been that way forever. But one autonomous car kills one person and it's the top story.