Agassi decided to stop taking meth, thus demonstrating his free will to do so.
Heroin does provide recreation for most users - it feels good, at least at first. Most don’t take it as medication.
Heroin users also prove their free will to use or not use heroin, by quitting heroin use.
Probably most illegal drug use falls into the “feels good” category.
As a person in recovery for 13yrs, I can tell you that really don't know what you're talking about.