Conrad parodies Europeans’ dishonest, self-righteous justifications for imperialism through Mr. Kurtz’s famous pamphlet about “the Suppression of Savage Customs.” Marlow describes the pamphlet like this:
[Kurtz] began with the argument that we whites, from the point of development we had arrived at, ‘must necessarily appear to them [savages] in the nature of supernatural beings—we approach them with the might of a deity,’ and so on, and so on. ‘By the simple exercise of our will we can exert a power for good practically unbounded,’ etc., etc.
Kurtz is a legend in the Congo largely because, unlike all the other ivory traders, he claims to be driven by principles. According to Marlow’s characterization here, Kurtz believes that Europeans are obviously culturally and morally superior to Africans, just like gods would be to Europeans. Therefore, Kurtz thinks, Europeans have an obligation to impose their superior culture on Africans through force. If Africans don’t want to be subjugated and converted to European ways of life, according to Kurtz’s line of thinking, this is merely because they are too ignorant to know what is good for them. Thus, Kurtz portrays conquest as a moral good, a way to improve Africans’ lives.
This attitude was relatively common in the late 19th and early 20th centuries, as European intellectuals looked for justifications for colonialism. In fact, when Marlow first set out for the Congo, his aunt told him something similar, which shows just how common such ideas were: she praised him for going to “‘wean those ignorant millions [of Africans] from their horrid ways.”
But Conrad believed that all of these justifications were just thinly-veiled excuses for Europeans to irresponsibly brutalize the rest of the world. By declaring that their own culture is superior, Europeans can conclude that might makes right, meaning that they are conquering other people for their own good. Through this reasoning, they can justify absolutely anything—including plunder and slavery—as part of their “civilizing mission.” Conrad criticizes this corrupt, self-serving logic by parodying it through Kurtz’s writings and actions. When he shows Kurtz make even more emphatic versions of the same arguments, but then turn out to be a liar and megalomaniac instead of the noble “emissary of pity, and science, and progress” that everyone else seems to expect, Conrad accuses real-world imperialists of pursuing exactly the same nefarious goals.