Considering that "impaired drivers" cause one-third of the traffic fatalities (over 12,000 a year), and also considering the fact that alcohol related crimes are estimated to cost over $200 billion a year, it's a wonder that states have not criminalized the act of serving alcohol to inebriated patrons.
Actually, they have.
According to a 2009 NHTSA study prepared by the Pacific Institute for Research and Evaluation (PIRE), nearly every state and the District of Columbia prohibit sales to intoxicated people (known as SIP laws). However, there is considerable variation among state laws both in terms of language employed to describe intoxication as well in defining what it means to "provide" alcohol. Further complicating things is the fact that states vary as to the level of proof required to prove guilt as well as who can be held liable for a violation of a SIP law.
States often employ two types of penalties for those found to have provided alcohol to an intoxicated person: administrative and criminal. The administrative penalties – fines, suspensions and revocations -- will only apply against individuals who serve liquor under a liquor (or other state-granted) license. So, a friend who hosts a party would not be subject to these penalties. Criminal statutes generally apply to all persons (although in 18 states it only applies to licensees and servers, thus generally removing noncommercial providers from liability). These criminal statutes also require a higher standard of proof – proof beyond a reasonable doubt.
This issue adds to the confusion of enforcement. An example of one state's law defines "intoxicated" as "a condition in which a person has drunk enough alcoholic beverages to observably affect his manner, disposition, speech, muscular movement, general appearance or behavior." Nebraska provides the most comprehensive definition by providing a list of visible intoxication indicators such as:
When state courts interpret these laws, it's not always clear what level of intoxication is required. For example, a Connecticut court held in one case that the term intoxication requires something more than merely being under the influence of alcohol, but in a later case clarified that a violation does not require showing that the person was "dead-drunk."
The PIRE Study found many reasons for lack of enforcement. Some were cultural – our country has a certain tolerance for excessive drinking. Some were practical – budgetary restrictions for law enforcement. And some were statutory -- the laws are not clear enough to make for consistent enforcement. In addition the penalties and fines – rarely resulting in jail time -- were insufficient
The PIRE study discusses a promising enforcement strategy for addressing SIP law violations. The first involved collecting "place of last drink" information for all DUI arrests (that's being done in Washington State and Utah) and targeting undercover SIP investigations to establishments identified by local law enforcement as "problem locations."
Considering the lax enforcement and relative ambiguity of these laws, it is unlikely that a SIP law will be enforced against an alcohol provider solely because a patron is found guilty of a DUI.