The question is, does it reduce the amount of attention paid to a significant enough degree that it's dangerous? Consider subways -- most of them have automatic train control systems in place that could effectively drive the trains automatically. However, operators are still required to control the speed, largely because it keeps them engaged.
Give an operator nothing to do, and they won't pay attention -- this is basic human psychology (look up "Vigilance Tasks" if you're interested in further reading).
The accidents will instead get caught up in that antivaxxer Facebook debate on their phones.