The potential benefits of allowing responsible alcohol consumption might be more than you think, if it helps provide a relaxed atmosphere where people want to go to work and are less likely to jump ship to your competitor for a marginal pay increase.
Providing alcohol to your employees or permitting them to consume alcohol on the job or at a company-sponsored event creates a whole host of potential liabilities. Here are a couple of real-world examples:
http://www.riskandinsurance.com/story.jsp?storyId=533353814
http://www.mmdnewswire.com/faapuna-mac-manu-mahoney-law-grou...
If you believe that alcohol is a good way to create a "relaxed atmosphere" let me assure you: there's nothing relaxing about watching your insurance premiums skyrocket, spending hundreds of thousands of dollars on attorneys, paying millions of dollars in damages and/or living with the fact that you were involved in an incident during which someone was seriously hurt or lost his or her life.
It is interesting that there doesn't seem to be the lawsuit worry or even the worry about "living with the fact that you were involved in an incident during which someone was seriously hurt or lost his or her life" at European companies.
Keep in mind that when a lawsuit is filed, the strength of your defense doesn't matter if you don't have the funds to pay a quality attorney. In many kinds of cases, you can easily rack up tens of thousands of dollars in legal bills before you even begin to address substantive matters, and plaintiff's counsel has no incentive to approach the matter in a fashion that reduces your costs.
[1] http://www.xperthr.com/news/marriott-ruling-highlights-risks...
[2] http://www.tprglaw.com/wolowsky-v-bum-steer-restaurants-inc
One potential benefit - you signal to employees that your workplace is fun. Many growing companies will die if they don't get the right talent. Compare the large risk of getting the wrong people to the tiny risk of an employee getting drunk and raping/murdering everyone, and the calculus is far from clear.
No business can eliminate all risk, but some risks are unnecessary and easily eliminated. Serving alcohol to employees creates a significant amount of potential legal liability (it could literally bankrupt your company) but it is hard to reasonably and objectively argue that the potential liabilities are outweighed by any of the potential benefits.