You still have to rely on other drivers not being actually suicidal. Just to give one terrifying example scenario: you will pass hundreds, if not thousands of other drivers driving in the opposite direction in the course of a long journey. Any motorist driving in the opposing lane has the ability to engage other drivers in a head-on collision at any time by making a relatively trivial maneuver. Given human reaction times, and the very high closing velocity of such a collision, you ability to avoid this would seem to be non-existent. You certainly couldn't "just stop" to prevent it.