As someone who has been in therapy for years because of being on the receiving end of narcissistic abuse, I can tell you that it's not just a case of, "there's some narcissism in everyone". Everyone has some degree of selfishness, but they have a well developed moral core because their parents raised them right. The difference between the average person who goes through periods of displaying narcissism and a true narcissist is that the latter never stops.
Narcissists get created by parents who are overly concerned with focusing on and awarding superficial characteristics, without conveying the warmth and unconditional love that children need to feel secure in themselves. It creates a performative-based personality who constantly seeks validation through projection, to fill a void that will never be filled. Their insecurity never goes away and they control everyone and every thing in their environment so that they can feel good about themselves. They will suck you dry of all emotional energy and then ditch you when you no longer have anything left to give, looking for the next supply. That's what happened to me. I was engaged to a narcissist.
A lot of children are raised in narcissistic environments, but many don't become narcissists. The reasons why some do and some don't are unclear.
Yes, a lot of drug users are narcissists, because drug are one way to artificially feel good about oneself... but it doesn't mean that all drug users are. Drugs amplify what is already there, they (mostly) don't create new pathologies. Eventually the high ends and then you come back down to earth, and when you do, if you have a solid secure inner core, then you won't be returning to insecurity. If you don't have that core, then as a narcissist you will immediately start your next validation seeking activity.
As part of my healing, I communicated with narcissists online who were professionally diagnosed by psychiatrists. My narc convinced me that I was the narcissist, when I actually was the one being fed on. All the narcissists I spoke to - as well as what I learned through reading the literature - told me that narcissists rarely get better. It takes years and years of therapy to even make a dent in it. Narcissists aren't near as a bad as psychopaths, but what they share in common is that they are pretty much incurable. They lack true empathy.
My narc was very skilled at displaying charisma and empathy, but it was all a ploy to get what he wanted. He never truly gave a shit. When I started to catch on, he gaslighted me.
Narcissists are toxic as fuck and I can smell them a mile away now. You're right, a lot of people display narcissism, because our consumer capitalist society was created by narcissists to make people feel ashamed unless they are constantly buying products. So narcissism is rewarded... how good you look, smell, act, how you "display" fitness, etc. But true narcissism as a pathology can only be taught in childhood. It is a pathology of 100% nurture. You're not born with it, you learn it.
