Full Idea
I cannot deny all respect to even a vicious man as a man; I cannot withdraw at least the respect that belongs to him in his quality as a man, even though by his deeds he makes himself unworthy of it.
Gist of Idea
We must respect the humanity even in a vicious criminal
Source
Immanuel Kant (Metaphysics of Morals II:Doctrine of Virtue [1797], 463 I.II)
Book Reference
Kant,Immanuel: 'The Metaphysics of Morals', ed/tr. Gregor,Mary [CUP 1991], p.255
A Reaction
The obvious way to find some respect for a vicious criminal is to ask how they got that way. Their state is almost certainly self-destructive, and not what they would ever have wished for. Would they choose eternal recurrence?