Actually we are told TO judge, unless we are engaged in the same behavior. How can a Christian try to lead a righteous life, or try and bring people to Christ, without judging between right and wrong behaviors?
We can judge behaviors. We are not to "judge" the souls. That is God's place. I believe a serial killer and/or rapist should be put to death for his crimes (judging his behavior). But I am still supposed to avoid wishing his soul go to hell, for I know not what is his heart at the hour of his death (judging his soul).
In this way, we are to hope the killer truly repents and his soul is forever cleansed....right before they inject the lethal serum that will end is treacherous, earthly life. We can forgive him and let the laws of man do what they must.