What do the narrator’s descriptions of former explorers lead you to believe about the reception of explorers during colonial times?

Marlow continues to talk of olden times when the Romans arrived and brought light, which even now is constantly flickering. He thinks what it might have been like for Romans to civilize a savage place like England. FRom this brief bit of text we might believe that explorers were a good thing. Marlow's grizzled appearance shows differently as he launches into his story about the Congo and the white devils (colonists) that used the people and resources, then spit them out.