This is really easy to explain: all of the colonial empires were horrifying engines of atrocity, oppression and death. Since imperial apologists hated socialism, that made it a very attractive ideology -- if the worst people alive hate something, it's got to have something to recommend it, right?
The Madras famine of 1877 (in which over 8 million people died) is characteristic. The British Empire didn't just fail to help, it actually made it illegal to offer food relief, on the grounds that it would distort the labour market and violate free-market principles. If you witnessed that, wouldn't you think the market and Moloch were one and the same?
It's worth noting that "concentration camp" is not the English translation of "Konzentrationslager": it's actually the other way around. The German word is the translation of an English phrase used to describe the British Empire's interment camps in the Boer War. IMO, it's impossible to look at, say, a picture of Lizzie van Zyl and not see a premonition of the Holocaust.