In battle, combatants engaged in war against America get no due process and may lawfully be killed. But citizens not in a battlefield - however despicable - are guaranteed a trial by our Constitution. No one argues that Americans who commit treason shouldn't be punished. The maximum penalty for treason is death. But the Constitution specifies the process necessary to convict.
But let us not forget that human love and compassion are equally deeply rooted in our primate heritage, and in this sphere too our sensibilities are of a higher order of magnitude than those of chimpanzees.