I didn’t care how lonely I felt if I had heroin, and being involved in that “scene” meant meeting and interacting with people who were in similar (crap) situations to myself, which we bonded over.
The Rat Park experiments showed us that well-socialized rats were less likely to develop addiction to cocaine than socially deprived rats.
"Researchers had already proved that when rats were placed in a cage, all alone, with no other community of rats, and offered two water bottles-one filled with water and the other with heroin or cocaine-the rats would repetitively drink from the drug-laced bottles until they all overdosed and died. Like pigeons pressing a pleasure lever, they were relentless, until their bodies and brains were overcome, and they died.
But Alexander wondered: is this about the drug or might it be related to the setting they were in? To test his hypothesis, he put rats in “rat parks,” where they were among others and free to roam and play, to socialize and to have sex. And they were given the same access to the same two types of drug laced bottles. When inhabiting a “rat park,” they remarkably preferred the plain water. Even when they did imbibe from the drug-filled bottle, they did so intermittently, not obsessively, and never overdosed. A social community beat the power of drugs."
The "Follow up experiments" section of the Wikipedia article somewhat contradicts you:
> Studies that followed up on the contribution of environmental enrichment to addiction produced mixed results. A replication study found that both caged and "park" rats showed a decreased preference for morphine compared to Alexander's original study; the author suggested a genetic reason for the difference Alexander initially observed.[9] Another study found that while social isolation can influence levels of heroin self-administration, isolation is not a necessary condition for heroin or cocaine injections to be reinforcing.[10]
> Other studies have reinforced the effect of environmental enrichment on self-administration, such as one that showed it reduced re-instatement of cocaine seeking behavior in mice through cues (though not if that re-instatement was induced by cocaine itself)[11] and another that showed it can eliminate previously established addiction-related behaviors.[12] Furthermore, removing mice from enriched environments has been shown to increase vulnerability to cocaine addiction[13] and exposure to complex environments during early stages of life produced dramatic changes in the reward system of the brain that resulted in reduced effects of cocaine.[14]
> Broadly speaking, there is mounting evidence that the impoverished small cage environments that are standard for the housing of laboratory animals have undue influence on lab animal behavior and biology.[15] These conditions can jeopardize both a basic premise of biomedical research—that healthy control animals are healthy—and the relevance of these kinds of animal studies to human conditions.[16]
My guess (haven't read the book): humans are social creatures, and too much company with just our own thoughts is not healthy in the long run. It might not cause addiction by itself, but it's definitely a disrupting factor for mental health. Interaction with other humans can help to interrupt unhealthy thought loops and help people to reflect on their state of mind.
