I'd be fucking pissed if there are bands who seriously fuck up due to the use of alcohol prior or during the show. These guys have a job to do. People pay their hard earned bucks to be at those shows, and deserve to get that proper show they are expecting.
That said, I never really like to go to any show in Amsterdam, simply because 25 to 30% of the bands get stoned, because they feel they're in the drugs capitol of europe.
Bands that do drugs or alcohol after the show, great no problem. I even showed the guys of american head charge to a coffeeshop, and smoked some with them. But that was AFTER the show.
When you show up drunk on your work, you get fired. But when you get home at 5 you can drink till you pass out, as long as you've sobered up the next morning.