I have no problem killing child rapists, but there may be unintended consequences to upping the punish to the ultimate level. The child rapist now has no incentive to leave the child alive if the punishment is the same for leaving him or her alive or not.

There's very little objective evidence that child rapists were raped as children. The data is gathered by psychologists, often in prisons, via "self-reporting." Often these alleged doctors are young, quite often attractive females. There's a huge motivation for the bastards to lie.