A distinction must be made between social interactions and social relationships. The schizoid, the narcissist and the inverted narcissist - all interact socially. But they fail to form human and social relationships. The schizoid is disinterested and the narcissist is both disinterested and incapable due to his lack of empathy and pervasive sense of grandiosity. The latter includes all our defense mechanisms and most of the superego.
Culture dictates what is to be repressed.
It is a vicious circle. One of the main stressors of modern society is alienation and a pervasive sense of isolation. These, of course, are many of the same designations that Lasch employs to describe the culture of narcissism. Thus, it appears, that it is not misleading to equate narcissism with schizoid disorder. Still, it is worthwhile to isolate the theoretical foundations of any equation between narcissism and the schizoid disorder.