If you take Darwinism to its logical conclusion, your goal should be to get you and your off-spring to survive. This would be accomplished by removing crimminals from society and the genepool. Since this is not really being done, I would say darwinism has not had much of a direct impact in this area.
It seems to me what has affected the justice system more is the Post-Modernist notion that everyone is inherently good. The only reason they do "antisocial" things is that society has treated them badly (like what happened to Frankenstein's monster-originally, it was the epitome goodness and love untill everyone rejected it).
Thus, the idea is to reform them, to make them tolerant individuals.
Also, since values are relitive in this system, you don't want to give some one too stiff a punishment, since who are you to decide what is true for some one else?
And if it is not the crimianal's fault that he did whatever, but society's, it would be unjust to give him any punishment beyond therepy anyway.
That is my opinion, since you asked.