Sure, some people definitely have malfunctioning opioid signaling but that issue is separate from someone who doesn't and they develop a heroin addictionAnd in some cases, the drug helps the plant/animal/person function better.
I was a lot more physically & socially active when I was on opioids. I could perform laborious tasks easier & better than without them.
It also cured my perpetual insomnia & horrid depression.
I think what's difficult about this subject is a lot of people confuse addiction & dependency. And the fact that the word "disease" is often a word used for a variety of illnesses. But usually when I think of a "disease", I think more of things like autoimmune problems, an illness, cancer, etc..
I think addiction could be a mental illness, but addiction is also incredibly complex.
If some one takes heroin 3 times a day & rarely escalates or abuses it, but wants to use it, does this make them an addict?
Compared to say.. some one who's throwing their entire life & resources away just to get a hit?
I'd say mental illness is the real cause & addiction is just a symptom or side effect of that.
But even mentally well people can end up with "addictions".
I think it's mostly just so big pharma can capitalize on it with new drugs too. But in a way it's good to at least recognize addiction/dependence as a health issue instead of just a criminal or moral failing.
In the second case, that is not a disease but rather a learned behavior