Whatever the reason and whatever their function,
why is the human nervous system vulnerable to so many different addictions? Its sort of like the unexpected opportunities for security breaches present in computer systems. It looks like no one can design an operating system that someone else can't hack.

Is this an unavoidable design flaw in all data processing systems, even biological ones? Is it unavoidably built into to all thinking machines? I couldn't follow much of that article, but it appears opioids have a long evolutionary history.

In a possibly related observation, it has been suggested that narcotic plants were selected by human consumers and that drove their evolution to produce more and more addictive and more potent psychoactive substances. That certainly seems to be the case with cannabis, although it is not addictive. The better the weed, the more likely users are to save the seeds and cultivate that strain.

Yes, Evolution works in mysterious ways.