He makes a good point about those people but the title of his book is a Mirror for the *Nihilist* Prince. Do those bugmen enhance the value of a prince's realm? The Christian case for preserving their lives is clear; what's the nihilist case for it?
You can guard your realm against the damage these people do until the end of time or you can set your realm up to weed these people out - gently or not - you're a nihilist, remember?