Does anyone ever become a heroin addict by choice?

Unlikely. I don't think people wake up and think, "i'm going to become a heroin addict today". People become heroin addicts because they like the way they feel on heroin, they have a genetic predisposition toward opiate addiction, and usually (but not always) they are not coping well with the problems in their lives. Some may be depressed and self destructive to boot, but no one asks for addiction.