One could hardly find a clearer expression of the modern rational mind’s fear of the unconscious than in Frazer’s statement about the universality of magic in primitive belief systems:

The dispassionate observer, whose studies have led him to plumb its depths, can hardly regard it otherwise than as a standing menace to civilisation. We seem to move on a thin crust which may at any moment be rent by the subterranean forces slumbering below.

It’s no wonder that Lovecraft, with his lurking horrors from the deeps of time, caught the nervous imagination of his time.