Don't need to assume. Every driver is either too incompetent to drive properly or intentionally trying to cause accidents.
Several months back someone ran me off the road. It was night, raining, and I was going about 65 mph on the highway. They hit the front of my car while moving from the lane next to me. I spun across three lanes of traffic, at one point staring directly into the headlights of another car, but by some miracle I didn't hit anything. I know they did it on purpose, too, because they were tailgating me for several miles and flashing their highbeams at me.
There was another time when I was driving on windy, hilly backroads and a car behind me kept speeding up until it was almost touching bumper to bumper, then it was back away and do it again. There were lots of very steep hills around and I had to pull off the side of the road into a ditch to keep this crazy (probably drunk) person from killing me.
I hate driving.