Having a car-dependent society means that all kinds of people will be driving under all kinds of conditions. People under stress, disoriented, emotional, etc. It is easy to say "people should be responsible," but where do you draw the line? Taking that bumper-sticker thinking to its logical conclusion, we should not waste money on stop signs or traffic signals.
Instead, why not just design a system that is safe for humans under a larger range of circumstances? For example: make public transit free, plant gardens of vegetables and flowers in every other street, and abolish the private auto.