So you believe Christ paid the sin debt and satisfied the justice of God for Hitler and Stalin?
He paid the sin debt for EVERYONE - he took away "the sins of the world."
The issue since the cross is not what we do that is "right or wrong" but what we do with Christ. The only issue in time and eternity is whether one has believed in and received Christ. Christ, not the law, is the standard of the new covenant of the New Testament.
So the question is what did Stalin or Hitler do with Christ.