In Out of the Silent Planet by C. S. Lewis, what are some of Weston's fears?

Out of the Silent Planet is the first of what is known as The Space Trilogy or The Cosmic Trilogy.  Dr. Weston and Dick Devine are travelers to the planet Malacandra.  

Though Dr. Weston is somewhat barbaric and aggressive, he fears the seroni. The seroni, or sorns, are humanoids with a highly developed sense of the scientific and technical aspects of life.  He fears them so much that he is willing to bring them a human sacrifice - Dr. Elwin Ransom.

Weston also fears the primitive inhabitants of Malacandra.  His speech, in chapter 20, is a manifestation of that fear.  He denounces their primitive ways as a reason to seek their annihilation.  Rather than admit his own primitive ancestry, and allow the beings of Malacandra to develop, he sees it as his mission to "cleanse" the planet.