Should Children Be Executed?

One of the classic Catholic justifications for the death penalty is the state's duty to protect its own citizens from harm (CCC 2265, Aquinas,  ST IIa-IIae, q. 64, a. 3). Traditionally, the state is permitted to execute a citizen for the same reason a state is permitted to execute an invader - in both cases, the state is bound to protect its own citizens from danger.

But, traditionally, a person who cannot distinguish right from wrong was spared execution. 

This is objectively absurd. Someone who knows right from wrong but doesn't care is, from the POV of outcomes, no different from someone who cannot distinguish right from wrong. In both cases, the person will do evil. Sure, the first is morally culpable and the second is not, but in both cases, citizens will come to harm precisely because evil will not be distinguished from the good, nor will evil be avoided.

Thus, if the state truly has a duty to protect its own citizens from harm, the state has a duty to execute both the one who chooses evil instead of good AND the one who cannot distinguish evil from good. The child and the child-like must be executed not because they are guilty, but because they are mortally dangerous. 

And, indeed, since the death penalty is about protection, not about revenge, it would seem morally better to execute the child-like if only because it so clearly isn't about revenge for their evil-doing (for we know they are not guilty in any classical sense) but definitely about preventing future evil so as to protect the population from further harm. 

That is, we do not execute children, true, but we do not execute them ONLY because we are assuredly more powerful than children. We can, unquestionably, restrain children from doing ignorant evil. However, if the person in question is very powerful but child-like in his moral reasoning, that is, if he cannot certainly be restrained by more powerful and more morally good men, then the morally good men have a duty to remove the powerful, child-like ignorantly evil man from their midst. 

Thus, the legal defense non compos mentis has no bearing on whether or not the person should be executed. If we are truly executing a person to avoid having evil wreaked upon innocent citizens, then it isn't a question of mind and choice, but rather of power to do evil, and likelihood that evil will be done.