You forgot the classic -
"I work hard - I just wanna have fun!"
I HAVE to drink (or drug) for my work!
The addict insists that he will not be able to make a living or that he will no longer be successful if forced to "give up" the increasingly harmful and destructive behaviors caused by his addiction. He may regard the latter as "the cost of doing business." In the vast majority of cases, of course, his addiction has already begun to impair his work performance, his judgment, and his interpersonal relations.
I actually think this is a serious and legitimate problem in some sectors for many people giving up drinking. I work in IT consultancy, an area known for its high percentage of males, long hours and drinking, and with a managing director in a very small company with a "work hard/play hard culture", full of hard drinkers and an MD who "invites" us to the pub after work regularly it is difficult to say no.
I know people who work as traders and analysts in Financial Services in London, and due to the stresses and classic bravado in it, that culture is known for its drinking and drugs element. If one's colleagues and bosses are all in the pub meeting or networking with clients and other bosses over the champagne and fine beers after work, it can be very difficult and maybe even somewhat detrimental for your career advancement not be with them...
Maybe the best way to stay sober when working in those sorts of environments is to look at a career or employer change...