You have to put it within context.
Big time "music stars" are exposed to a level of drug and alcohol consumption that most people will never reach. So it makes sense that they would've have some bad experiences with those things that your average person wouldn't ever have, so their perception of it may be skewed a bit compared to the "normal experience"
For instance, for most who like to have a few beers and smoke the occasional joint, that doesn't often get followed by an invite for "come to this penthouse party at the Ritz Carlton later where there will be hookers, heroin, and $25,000 worth of cocaine all cut up and ready to go".
I'm someone who's enjoyed craft beer (and maybe the occasional toke or two) over the years... I've drank to excess (where I've thrown up) literally one time when I was in college, and that's been the extent of it.
Aging rock stars lecturing people about the dangers of alcohol and marijuana smacks of that stereotypical parent who enjoyed themselves, but then tells their kids "well, uh...learn from my mistakes, there's nothing good that can come of it" lol. Easy for them to say after they've got to have all of their fun.
To me (and yes, I know these fellas aren't popular with some folks), guys like Bert Kreischer and Joe Rogan have a more realistic take on substances than puritanical types, or aging rock stars who decide to become completely "straight edge" after having some bad experiences.
I think the reality is, if kept withing moderation, certain substances can be enjoyed, and enjoyed with no serious long-term ill effects.