Imprisonment is completely Islamic and humane!
5:33 The just punishment for those who wage war against God and His Messenger and endeavor to commit bloody crimes on earth, is that they be killed or crucified, or have their hands and feet severed on alternate sides, or to be banished from the land. Such is their disgrace in this world, and an awful suffering awaits them in the Hereafter.
[Fasaad = Bloody crimes = Spreading corruption in the land = Creating disorder. 'God and His Messenger' … None can physically fight against God, and the Messenger was a mortal man. So, God and the Messenger denote the Central Authority of the Islamic State. Waging war against God and the Messenger would mean rebellion against the Islamic State. 'Severing the hands and feet' may also be understood as cutting of their ability to create Fasaad. See 5:38 & 12:31. 'Banishing from the land' may indicate exile or IMPRISONMENT for life. If they present to the authorities before getting arrested, they could be pardoned. 4:64]