the world wars really fucked a lotta people up. there was this attitude that through technological advancement, humanity would transcend our frailties, and well...nothing is ever that simple, but a lot of people couldn't accept that, so they swung in the other direction, basically deciding humanity was too sick to survive in its current form (see dadaism in art as an example). we're not on the third or forth generation of people bent on either transforming humanity or wiping it out entirely.