My response to that is to assert that most of the negative impact of the opiate crisis is due to the fact that people become addicted to them and are then unable to obtain them through legal means, which effectively forces them into criminal activity.

I'm certainly not saying opiate addiction is a neutral/good thing, but I don't think it would cause the societal harm that we see today with them being tightly regulated.

Potential case in point: illegal methamphetamine usage/addiction is a huge issue today in the US. I qualify that as "illegal", because meth is available by prescription under the trade name Desoxyn. Many drugs with similar effects are likewise available and much more commonly prescribed - but I'm not aware of anyone calling for them to be banned. If anything, I suspect in that case the overall societal impact is positive: I know I would be much less effective as a developer if I were to lose access to ADHD medication.