To understand the ideology that underpins far-right protests against refugees and asylum seekers, a good starting point might be the great American novel. Near the start of F Scott Fitzgerald’s The Great Gatsby, published in 1925, Tom Buchanan is mansplaining. “If we don’t look out,” he announces excitedly, “the white race will be – will be utterly submerged. It’s all scientific stuff; it’s been proved.” Those words are, with minor variations, repeated now in Ireland by people who adhere to the increasingly mainstream theory of the Great Replacement. It, too, is “scientific stuff”, harvested from social media. It “proves” that...