I agree with most of your comment, but I think there are a few inaccuracies worth pointing out.
> The thing is, being a rockstar is ... [about] using drugs to dull the loss of identity caused by never being in the same city for more than 6 hours.
I am not entirely sure that's the root cause for rock stars' drug use. It's certainly part of it, but in large part it's intimately tied to the socialization context that surrounds the entire rock scene.
When a fan is going to a show, it's a special event. A large population of those fans use drugs in an effort to enhance their enjoyment. They also want to share that enjoyment with the band, and they are quite willing to share their supply with the band. In other words, the rock band basically has a free, unlimited supply of drugs and a social expectaton to take advantage of that.
> There's a reason why they all act so damn crazy after a certain point in their careers.
I'm sure you didn't mean that literally, but there are several rock stars who don't end up crazy. Led Zeppelin, Brian May (a PhD!), BB King, Buddy Guy, Ben Folds, Nickelback, Darius Rucker (Hootie), I could go on forever... The reality is that it's a small subset of rock stars that go crazy, and I would argue that the proportion is actually lower than for the average population of somewhat-heavy drug users.