Even if some people are predisposed to drink heavily, that tendency does not explain how they act when they drink. Does anyone really believe that alcohol made Mel Gibson temporarily anti-Semitic, causing him to rail against the Jews when he was pulled over in Malibu for drunk driving? Or that Bob Ney, the Republican congressman from Ohio who mentioned "a dependence on alcohol" when he pleaded guilty to corruption charges, was driven by demon rum to accept lobbyists' goodies in exchange for official favors?
There is another way of understanding such cases, reflected in the aphorism "in vino veritas." According to this theory, alcohol reveals the true you.
But as the psychologist Craig MacAndrew and the anthropologist Robert Edgerton observed in their classic 1969 study of the subject, that cannot be the whole story. "With alcohol inside us," they noted, "our comportment may change in any of a wondrously profuse variety of ways ... How can the conventional understanding of alcohol qua disinhibitor possibly accommodate the fact that even within our own culture people who have made their bodies alcoholled differ so drastically both within and among themselves in their subsequent doings?"
Looking at differences in "drunken comportment" across settings, MacAndrew and Edgerton concluded that context plays a crucial role in determining how people behave when they drink. In particular, cultural expectations -- "what their society makes of and imparts to them concerning the state of drunkenness" -- can be the difference between violence and peace, surliness and sociability, loud lust and quiet contemplation. If we expect drinking to cause bad behavior, we help make it so.