OK, let's follow your logic.
- addiction is "a 100% avoidable and self-inflicted disease"
- so no-one, ever, under any circumstances, should
: drink alcohol
: smoke or otherwise use tobacco
: take over-the-counter meds
: take any prescription medication that is mind-altering, for any condition

And, 
- no-one, ever, under any circumstances, should
: be young
: be foolish
: be a risk-taker
: be depressed, angry, abused, or otherwise in mental or emotional pain

Interesting, by the way, that you only speak to the "demand" end of the problem, not the "supply" end, particularly when pharmaceuticals and other 'legal' drugs (like alcohol, tobacco, OTCs) are concerned