Most people with a license understand that there's some risk inherent in the process of driving a motor vehicle. Every time you get in a vehicle, whether as a driver or a passenger, there's the potential for something to happen. Your vehicle could have mechanical issues that result in loss of control. Inclement weather could make the roads unsafe. You could also cross paths with someone who isn't making safety on the road a priority.
Unsafe drivers who get behind the wheel while intoxicated, exhausted or distracted put everyone else on the road at risk. Their driving practices dramatically increase the risk of a crash for them and everyone else on the road with them. When those unsafe drivers are in charge of massive commercial vehicles, the end result could be tragic.