What do you think the situation is that led up to the story the chrysalids?

Apparently it is a post-apocalyptic world, where nuclear weapons have been used, so the mutation/cancer possibilities are high. They have learned to avoid plants that don't look "normal," and also humans in order to survive have tried to only breed with other "normal" people. They have lost a lot of technology and a lot of knowledge, and they have reverted to fear and a fight merely for survival.

Some of the mutations have been good, and even the most repressed parts of society are starting to accept them slowly... and probably will continue to do so as life slowly gets better... but in this story a slow moving society is confronted by a faster moving society, and a large portion of the slower society is butchered.