Little devil's advocate here. As much as these guys deserve long painful deaths for their crimes, executing them would help their cause. Dead, they would be martyrs to be celebrated by fellow extremists. Keeping them alive in jail shows them as unable to defeat the Great Satan, kept alive in our system.
Hack into islamo-nazi communication sites and post security video of them in their prison uniforms, pacing their cell with it's open toilet, dependent on their enemy for food, clothing, shelter, prayer mats, ect. Sounds more demoralizing to me.