Funny enough, if I buy heroin on a street corner, the addiction is voluntary. If I get prescribed opioids and the doctor who I trust ensures me it's the right thing on my situation, I wouldn't call all cases "voluntary addiction".

Edit: I can buy a damn gun when I'm 18, but have to be 21 to drink beer and will never be allowed to buy LSD which is pretty safe and not addictive. WTF?! I blame religion and Puritan nut jobs.