The drink-driving death of Princess Diana highlighted the problem for many people. Unfortunately- at least in Australia- some people considered it to be caused by speeding. This was because the media focussed on the speed of the vehicle- particularly in the early days after the accident. This accords with their emphasis on 'speed related' accidents to try to make speeding tickets more palatable. Therefore, for many drink-drivers, the tragedy will not shock them into the awareness of their homicidal/suicidal behaviour that it could have.
The main reason drunk drivers kill people is that drinking slows down reactions. This slowing down of reactions is incredibly significant in context. To explain this, consider a situation where the reverse occurs with regard to reactions. If you drive faster, ergonomic research shows that you will have greater alertness and thus faster reactions. All things being equal, by driving faster your faster reactions would mean that you would brake sooner and thus stop sooner and have more time to react because you would notice problems faster and react faster. However things are not equal. The faster you drive the longer the distance it takes to stop once you brake and the faster the event rate around you. Thus going faster does not necessarily create an advantage. In the reverse situation- drink-driving - things are equal. The slower reactions mean that drunk-drivers are disadvantaged because neither braking distance nor event rate nor anything else change because of your Blood Alcohol Concentration.
Drunk-drivers can also become overconfident and drive in ways that demand high levels of skill. Their lack of coordination in this state makes this behaviour particularly dangerous.