One important point that a doctor makes in Dreamland is that if Oxy / heroin did not exist, all of the people who got addicted would still end up being addicts.
Their addiction would likely be to alcohol and it would develop later in life because alcohol takes much longer than heroin to wipe out an individual, but the addiction would still happen.
The issues that pushed these people to addiction would still be there, irrespective of whether Oxy / heroin ever crossed their path.
