I think it all depends on what the individual wants to present publicly to an audience. to drink or not to drink (in terms of the performance) is not much different than to rehearse or not to rehearse, to buy a new instrument or not etc. etc. All of these things can affect how you come across to an audience. I believe that comfort plays as big a role as anything. The drinking issue is different because there is always potential for drink/drugs to affect your health and well being so we look at that issue differently. If someone drinks/drugs to the extent that it affects their performance or their attitude during a performance, than it shows both lack of judgement and lack of caring about the audience. These are the performers I would soon stop going to see once I realized what was going on.

Frank