Conrad doesn't exactly want to buy the world a Coke, but he does seem to have some unconventional ideas about race—at least, unconventional for the late nineteenth century. In Heart of Darkness, he seems to be suggesting that there really isn't so much difference between black and white—except that this vision of racial harmony becomes more complicated when you consider that he seems to be suggesting that black people are just less evolved versions of white people. Maybe. We're like 50% sure on that one. As with most issues in Heart of Darkness, the differences between black and white are so confusing as to be almost meaningless. And, in fact, maybe that's just Conrad's point.
Despite white Europe’s good intentions towards the Africans and their desire to "civilize" the black man, imperialism proves to be a brutal and callous victimization of the native Africans for the sole purpose of maximizing profits.
Despite Kurtz’s brutality, he treats the Africans more civilly and more as equals than the majority of the other white European characters (like the accountant, the manager, and even Marlow). This is why Marlow sees him as the lesser of two evils.