Here's an interesting article about the connection between low level drugs (cigarettes, alcohol, marijuana) and the use of harder drugs. Admittedly, a lot of it is over my head, but I did get the part where they state that the use of cigarettes, alcohol, and marijuana make it 24 more times likely someone will use hard drugs.
What caught my eye was the short section on the two competing theories as to why lower level precede the use of harder drugs.
There are two general schools of thought on the gateway effect. The first is that the gateway effect is causal: Cigarette or alcohol use causes marijuana use and marijuana use causes cocaine use. If the gateway effect is causal, then smoking restrictions should decrease marijuana use and the legalization of marijuana would lead to an increase in cocaine use. The second school of thought is that the gateway effect is merely descriptive: Individuals have a preference for drug use and the fact that individuals typically use marijuana first is due to some unobservable factor, such as marijuana being more readily available.
Personally, I think the two theories intertwine in reality. I'm pretty sure every human comes wired to seek pleasure and starting out at a lower level can lead to attempts to repeat an action in a manner believed to provide greater pleasure. I'm actually more curious about what barriers prevent most everyone from moving up the chain until we're all hooked to a morphine drip.
I'd posit three strong reasons for this barrier affect (I'm sure there are a passel of small ones). First, social norms. Second, perception of danger. Third, anticipated opportunity loss.
To begin with, let's address the social norms. Here I think we will all agree that a large portion of the population - probably a majority - perceive cigarettes, alcohol, and Marijuana as falling in a normal to use category. Their downside is discounted to a certain degree and it is expected that almost everyone will partake of them - at least as young adults. The step up to the next level is not acceptable. Cocaine, heroin, and oxycodone are not seen as normal use and therefore use is viewed with with disapproval. These are norms handed down as part of the social atmosphere. You see Uncle Ted and Aunt Katrina smoking and drinking a beer; you don't see them using cocaine.
Perception of Danger
Next we come to the perception of danger. Cigarettes are known to have long term harmful consequences. Alcohol clearly has the ability to be dangerous in both the short term and long term, but is so ingrained in society that is part of religious functions and part of everyday life for most people without any serious problems. Marijuana has not been widely perceived to have large detrimental health effects. There is some perception that heavy use impacts intellect over time and one imagines that the inhalation of a foreign substance into a person's lungs can lead to long term health issues, but no one seems to take that into account. Consequently, there may be a perception of some minor danger, but there isn't a great feeling of immediate jeopardy.
On the other hand, even in depressed communities - perhaps especially in depressed communities - the affects of harder drugs become known. Heroin kills. Crystal meth makes you skinny, scabby, paranoid and dangerous. Everybody overdoses from fentanyl. Sure, some people will always go there anyway (after all there are no shortage of young people who think they are invulnerable), but a lot of people seeing what's happened to those before them will stop short. Additionally, I think the threat of incarceration has a lesser effect in causing people not to use the harder drugs.
Anticipated Loss of Potential
While I occasionally make fun of the young among us for not exercising their brains much, they are generally on a path and can see their potential futures. They can see that someone addicted to heroin or cocaine isn't as likely to succeed. Thus, when middle class or above kids are making their way thru high school and going off to college the majority of them don't come out the other end with addiction issues. And don't try to tell me that drugs aren't available in and around school; Lexington PD raided the place where kids congregated just outside my Junior High School when I was in the eighth grade. I had a classmate in college tell me how he had sworn off LSD because a building tried to attack him while he was high and walking across campus. Drugs are available while you are in school.
So, I see the minor drugs as a gateway of sorts, but the jump to harder drugs not being accomplished solely thru them. There has to be something that gets a person over the barrier. This could come in many flavors. There are always some few people who simply fall off the path because of they are young and (in their own mind) invulnerable or they have a major event and seek solace in oblivion or maybe they came equipped with a greater genetic predisposition. There are always people who have so much familial money/power they will be taken care of even if they turn into the biggest herion addict on the West Coast. Most importantly, if there doesn't appear to be a set path for success then immediate gratification becomes a much more powerful draw. This is your basic explanation as to why, despite not having the same level of general affluence, drugs are more commonly found in depressed communities where their economic impact is more profound.
There is an argument that in order to make the lesser drugs even less of a connection to the harder drugs they should be legal, affordable, and relatively easy to access. Minor entry level bumps (which are fairly easily worked around) may be acceptable to reduce their potential for harm, but making them so high that the lesser drugs go back to being sold by the same guy who is distributing coke, heroin, or oxys is counterproductive.
In fact, I've often wondered if - and at times posited that - the main reason that marijuana is a gateway drug is that it is sold by the same person who is selling coke and he'd really like to get you hooked on that more addictive drug to make you a more dependent customer.