You can't just ignore that some substances can have far higher physical and psychological addictive properties than others, independent of the user.
Even if drugs were legalised, after a decade I'd be willing to bet my house that there would still be FAR more alcoholics than drug addicts.
You're right though, we can't ignore the addictive properties of drugs, which is why education is so important.
I recall reading a paper a while back about the levels of dependency/addition on prescription drugs. it was astounding. Then add in the number of people who would "never give up booze completely, but I'm sure I could if i wanted to" and the millions of cigarette smokers.
We live in a bizarre state where one type of drug addiction is considered to be acceptable and others are not, simply based on historical legislation of that drug (compared to dry countries for example).
True, heroin addiction is all encompassing for many, but that's because there are few places to turn and even the places that you can only substitute one drug for another, state authorised one. It's a no win situation.