This is pretty obvious. Having a black box helps better understand what happened and what may need to change to avoid future accidents.
This is clearly different than always transmitting my speed and writing tickets without context.
The black box, by providing evidence to prosecute me, makes the roads safer for other people as while I'm in prison, I can't cause any further accidents. But it doesn't make me all that much safer, prison is a dangerous place.
The only time a black box ever gets used for that stuff is when an agent of the state or corporation with deep pockets to buy power or other "more equal animal" is trying to get one over of one of us peasants.
When speed is a serious factor it is generally obvious from the results of the crash anyway.