The premise of this entire book is that there is one type of human and that anybody who does not conform to that type or description is immediately rejected and made an outcast by this futuristic society. This is made clear very quickly through the example of Sophie, a normal girl but one who possesses a sixth toe which makes her a "blasphemy" and a "mutant," a "deviation" in God's sight. It is this sixth toe that is the reason for her forced sterilisation and expulsion from "normal" society into the Fringes. Note how the Inspector, the man responsible for deciding what is a mutation and what is not, explains the importance of reporting mutations to David:
You know, David, concealment of a Blasphemy--not reporting a human deviation--is a very, very serious thing. People go to prison for it. It is everybody's duty to report any kind of Offence to me--even if they aren't sure--so that I can decide.
The savage way in which Sophie is treated and also the way in which natural deviations are either burnt or slaughtered ritually shows us how this society feels intensely threatened by any difference and how swiftly they move to eradicate it.