It helps us bond with significant others, motivates us to raise children, to consume, to study, to explore, to discover, to invent, to innovate. It is a powerful engine of human personal progress. Pathological narcissism has very little to do with healthy narcissism. It is a malignant form of narcissism because it takes over the host and then kills it. You make NPD sound like a kind of parasite, both in the way the disorder impacts the narcissist himself, and in the parasitic attitude the narcissist then takes towards others.
Pathological narcissism is parasitism.
It is the unabashed, ruthless and unscrupulous exploitation of others as sounding boards, as accumulators of past glories, as servants, as extensions of the narcissist. The narcissist idealizes, then uses, then devalues, then discards. The narcissist colonises, then abandons. You seem to be saying that the desire for approval, which in the case of healthy narcissism is a kind of glue that helps create and cement relationships, becomes so overpowering as to destroy them altogether. Both healthy and pathological narcissism are part of the same developmental phase.