You presume that I would rather live longer and drink than live for a shorter time and not drink. I deliberately take actions which do not maximize my expected lifespan, because a day of my life has finite value.
For example, drinking 2-4 drinks will impair me for a period of about 2-4 hours. That is a statistically significant portion of the day.
I wouldn't call 2-4 drinks impairment... then again I don't often drink in a time span that I would otherwise spend doing productive or difficult things.
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.