I think that alcoholism as a genetic predisposition is as plausible as chocolate addiction having genetic roots. It isn’t unlikely, however, that there are certain chemical imbalances that are inherited which lead to certain dependencies or an outright addictive personality.
The reality of it is that people want to remove themselves from blame. Whether blaming an "obesity gene" or the latest "spontaneous anger outburst syndrome" (or something), if people have something to blame their weakness on they are no longer responsible for their shortcomings.
Additionally, since Lamarckian genetics was prove false long ago, spontaneous generation of genetic dispositions appearing in a few generations is not an accepted reality. The presence of alcohol in the grand scheme of the human time line is nothing more than a blip, a genetic disposition favoring alcoholism developing within those relatively few generations just isn’t realistic.