Everything being legal gives my behaviour a pass. But that's beside the point.
The article does include genetics as well as nurture.
It also states that a lot of it is unknown, so we cannot be definite.
"Several studies from across the world have demonstrated that narcissism is, at least partly, genetic—in fact, according to a couple of studies, the risk of inheriting narcissism is over 50% in some cases. Narcissism, like other conditions under the behavioral genetics umbrella, is often studied using twins."