I think the point in loosening up using alcohol before interviews, is to improve relaxation and, as a result, give a less awkward interview performance. The reason one might choose to do this is because interviews count for so much.
This has been compared many times to doing a challenging clinical procedure or having a first patient interaction. The implication is that, if one needs alcohol to calm nerves before an interview, why would that stop in other places? However, I think the comparison here is quite specious.
The main difference between an interview and other situations is that in an interview situation, one is not drinking to avoid the feeling of anxiety: one is drinking to avoid communicating the signs of nervousness that excessive anxiety may produce. In a clinical interaction or during a procedure, controlling for anxiety may be important but it is not crucial. With anxiety during a procedure one may, for example, perform better. And with anxiety during a first clinical interaction, one knows that this is part of the learning process.
In an interview, on the other hand, it is much more crucial to control anxiety, because the nature of the encounter is probably more negatively affected by anxiety than a procedure (where anxiety might help), or than a clinical encounter (where anxiety can be quickly overcome through practice and where awkwardness the first few times won't break a career).
Add to this the fact that, for many, interviews are possibly the most difficult part of the application process--and therefore the most anxiety producing--and we get a situation that is quite incommensurable with the many other varieties of stress.
With regard to alcoholism, if the OP were using alcohol to bring some sort of relief, it would clearly be bad. But if the goal is to improve performance, and they otherwise do not have problems dealing with stressful social situations, then some sort of drug, maybe not alcohol, but something, doesn't seem like such an awful idea. If other things are controlled for, it seems to me like a way, if not a conventional or socially well-regarded way, to do significantly better during the interview.
I think the major issue with doing something like this is having interviewers smell alcohol on the breath.
