Bottom line: while only a small proportion of those who become intoxicated do stupid or criminal things, a large proportion of all stupid and criminal acts are committed by people who are intoxicated, and bars are indeed public places.
One point that Clayton doesn’t make, in response to Glenn’s assertion that the obvious next step is giving people sobriety tests at home for fear they should then go out: Very few people actually sleep in bars. Sobering up occurs at the rate of about one drink per hour. Bars have parking lots because many patrons drive to them. A drunken bar patron has a very high likelihood of becoming a drunken driver when he leaves. Someone getting drunk at home has a better chance of sleeping it off safely.
I hope someone has noticed the terrific research opportunity the crackdown creates to discover whether such enforcement actually cuts down on the rates of drunken driving and drunken assault. Whatever the legal justification for the policy in question, it still ought to be abandoned if it doesn’t produce results.
Perhaps I should mention here my personal alcohol-policy hobbyhorse: a law to forbid the purchase of alcohol by those previously convicted of alcohol-related crimes.