Now for the other side. While all of the previous post is true, it does not mean allowing evil to run wild… or at all. While one can try to understand what is going on in the mind of a terrorist, or a criminal, that does not mean letting him do what he wants. We can not allow abusers, criminals, or terrorists to do as they please. If the only way to stop an impending terror attack is to torture a partner of the perpetrator, than do it. Not because of hate, but to prevent an evil act.
The Torah says that one who has pity on evil people, will eventually be doing a hateful act to innocent bystanders. As much as we need to “understand” those who are evil, we have first a mandate to understand the public’s need for protection. Society needs to impose penalties for crime, not only as a deterrent, but as Rabbi Moshe Feinstein said, as an indicator to the public of how wrong and immoral such actions are.
Understanding the evil person should only be used to try and solve the underlying problems. It should never be used to condone the evil intent or behavior.