The problem is that a drunk person is by definition incapable of making appropriate decisions about his behavior.
Perhaps the silliest thing about the whole "drunk driving" idea is the theory that someone will drive somewhere, get blasted and then be clearheaded enought to decide whether he should drive home.
Personally, if I plan to drink, I take a cab to the bar or party. Then I have no choice but to take one home or catch a ride.
No one forced him to get drunk.
Well, during my more heavy drinking days, I've tipped 15-20 beers back, was staggering, left my car at the place, and walked home, picking it up the next day.
So they are clearheaded enough to know NOT to drive home.