Stephen, as you yourself say, even the Nazi had what they believed were good moral justifications for what they did. And Christians have certainly being guilty of horrible crimes in the name of their God throughout history.
As for consequences, depends on what you mean. Obviously people should be stopped from harming others. But I don’t believe in retribution, I’d like to see a system of justice that is geared toward reformation, whenever possible. When not possible, we may need to restrain people, but in the most humane way available.