The first time I read the book, it sounded like a sardonic statement of how insane Kurtz had become.
Now it seems like the voice of the forest.
If it's natural for monkeys to be stupid, it's natural for those who have escaped that stage to slaughter all those of the previous stage -- so that evolution continues.
Looking at humanity... well, most of these idiots don't care about anything but their bread and circuses. Many are obviously genetic defects, or come from family lines that didn't make certain evolutionary leaps.
Purging them is a good idea. So is pushing ourselves farther so the next generations are much smarter than this one...