I don't think it would be right or proper to control for killing other people due to alcohol use even if you could. The social externalities of alcohol use are a separate question from the private benefits.
I agree that there's some merit to treating alcohol's effects on you and others separately, but if we do that, shouldn't we then also work to exclude some of its benefits as "social externalities"? Like the whole "alcohol -> socializing -> mental well-being"-pattern?
My roommate recently sent me a review article that LW might find interesting:
Personal observation says that LWers tend not to drink very much or often. Perhaps that should change, to the degree suggested by the article?
Full article here.