I think some people can drink socially with no problem, but if you are drinking on your job or while rehearsing, you definitely have a problem.
I used to think I couldn't sing without drinking because I had such bad stage fright, but eventually I got over it and can sing without drinking. Also, just getting up there and doing it over and over, eventually you feel more confident. If you're solid in your musicianship, you shouldn't need to drink or do drugs to feel capable.
Look at all the famous people who feel they need it, though, including singers, actors, musicians etc. Very sad.