I actually agree with you. Rapist genes should be purged. The baby is innocent, yes, but it's also actively harmful by simply existing. It harms the mother and father by being a constant reminder of the rape, and it harms society by propagating low IQ a low IQ rapist's bloodline. It even harms itself by having to live with the fact that it's a rape baby.

Besides, if you're a Christian you believe that babies go to heaven anyway. Unless you're one of the more hardcore branches, in which case it goes to purgatory, then heaven. Which is still pretty good.