What precisely is being criminalized? Not bad driving. Not destruction of property. Not the taking of human life or reckless endangerment. The crime is having the wrong substance in your blood. Yet it is possible, in fact, to have this substance in your blood, even while driving, and not commit anything like what has been traditionally called a crime.
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Now, the immediate response goes this way: drunk driving has to be illegal because the probability of causing an accident rises dramatically when you drink. The answer is just as simple: government in a free society should not deal in probabilities. The law should deal in actions and actions alone, and only insofar as they damage person or property. Probabilities are something for insurance companies to assess on a competitive and voluntary basis.
This is why the campaign against "racial profiling" has intuitive plausibility to many people: surely a person shouldn't be hounded solely because some demographic groups have higher crime rates than others. Government should be preventing and punishing crimes themselves, not probabilities and propensities. Neither, then, should we have driver profiling, which assumes that just because a person has quaffed a few he is automatically a danger.
In fact, driver profiling is worse than racial profiling, because the latter only implies that the police are more watchful, not that they criminalize race itself. Despite the propaganda, what's being criminalized in the case of drunk driving is not the probability that a person driving will get into an accident but the fact of the blood-alcohol content itself. A drunk driver is humiliated and destroyed even when he hasn't done any harm.
Of course, enforcement is a serious problem. A sizeable number of people leaving a bar or a restaurant would probably qualify as DUI. But there is no way for the police to know unless they are tipped off by a swerving car or reckless driving in general. But the question becomes: why not ticket the swerving or recklessness and leave the alcohol out of it? Why indeed.