The issue is, if you look behind the curtain, that while some drug users were successful, most users end up ruining their lives because of drugs. See: Hendrix, Joplin, Cobain (debatable by some), Morrison, Mike Inez (AIC Bassist, dead from overdose after years in rehab), Layne Staley... I can keep going.
I will argue that the personal habits and issues of the user directly relate to how a drug affects their lives, but in general they do more harm than good. Same with legal drugs and alcohol.
But I will agree that we wouldn't have a lot of our great music or comedy without drugs either. Its a double-edged sword that can't be put in black and white terms. Its a case by case basis.
Some people can handle their drugs, and be successful in life. Some people die directly or indirectly due to their drug use. Some just get screwed by a system that isn't designed to help them, just punish them for being human and having failings.
What you say is very true. Most who encounter these addictions are often plagued, and sometimes destroyed, by the demons addiction creates. Even Carlin, who was a big coke addict in his day, stated in one of his interviews with John Stewart:
This is the reason that I say I don't blame the drugs. Drugs are the tool. If you do not research or, at least, inform yourself of what drug you wish to use and then wind up becoming addicted and harm yourself or others...that is NOT the drug's fault. That is your fault for not being intelligent enough about the substances you choose to ingest or, in some cases, your fault for not having the courage to admit your fault and seek help and guidance to get you back on your feet.