Detaining people for shouting republican slogans, even if they do so in a deliberately coarse and provocative way, is utterly un-British [...] I worr… - Daniel Hannan

In an atmosphere when anyone can close down the conversation by saying “I feel uncomfortable”, rational discussion becomes impossible. The empirical method, the basis of Enlightenment civilization, no longer applies.

Eugenics, of course, topples easily into racism. Engels himself wrote of the "racial trash" - the groups who would necessarily be supplanted as scientific socialism came into its own. Season this outlook with a sprinkling of anti-capitalism and you often got Leftist anti-Semitism.

The two totalitarian systems [USSR Communism and German National-Socialism] traded in all the necessary commodities of war: not just oil and vital chemicals, but arms and ships. They exhibited each other’s cultural achievements, performed each other’s music and films, stressed their joint hostility to Western capitalism.