Well before the documentary, a Graybeard I know told me that way back in the early 50's, two hardware store new Rem 721's fired into the floorboards of a car, when the safeties were released.
On another forum a poster stated that a woman in El Paso had been killed, when an owner of a Rem 700 got home and unloaded his rifle in the driveway. The rifle discharged upon safety release, the bullet went way up, and way down, killing the woman who apparently was outside on the lawn.
The reason these things have triggers is so you can control when it goes off. Accidentaly discharges due to defective designs will kill people.
If I'm not shooting, I'm reloading.