Show No Pity, or Cultivate Pity?

One theme that has come up repeatedly in my reading of Deuteronomy is God's command to the Israelites not to pity certain people.  Specifically, God in Deuteronomy commands the Israelites not to pity the following: the Canaanites (Deuteronomy 7:16), an intimate who is encouraging an Israelite to worship other gods (Deuteronomy 13:8), someone who maliciously and intentionally kills another person (Deuteronomy 19:13), a false witness (Deuteronomy 19:21), and a woman who grabs a man's privates in an attempt to protect her husband (Deuteronomy 25:12).  The Canaanites, the idolatrous intimate, and the killer are to be put to death.  The false witness is to receive the punishment that he was hoping the person he accused would receive.  And the women who grabs the man's privates will get her hand cut off.

What I was thinking about as I read this passage was this: Shouldn't we be cultivating our pity, rather than suppressing it?  It seems to me that God (or people's characterization of God) expects for Christians to put up with so much garbage from people in this imperfect world with love, tolerance, grace, serenity, compassion, and forgiveness.  The cultivation of pity can help Christians on their quest to do this, for it can assist them in humanizing the people who do the garbage that annoys them, or that is just plain evil.  Christians can reflect that those who do bad things may perhaps have been victims themselves in the past, and so they are to be pitied rather than hated.  In light of this, Deuteronomy's command for the Israelites not to pity in certain situations slightly takes me aback.

And yet, Deuteronomy's tough stance makes a degree of sense.  How can God establish a holy people and get God's message off the ground if there are people----foreign and domestic----who are attempting to turn Israel from her God?  How can society be safe if people are maliciously killing others or are bearing false witness to get someone else into serious trouble?  I have a hard time accepting Deuteronomy's command that the woman grabbing the man's privates get her hand cut off, since she was just trying to protect her husband.  At the same time, her act could have had devastating consequences for her victim, for it could have deprived him of the ability to produce children.  This would run contrary to God's desire to make Israel populous, as well as deprive the victim of offspring who can work his land and take care of him in his old age.  Thus, it's understandable that Deuteronomy sought to discourage that sort of action on the part of women (but why not men?).

Should justice be tempered with mercy?  Deuteronomy screams "no" in the cases that I listed.  I don't think that most people would believe that those who hurt others should simply be let off the hook.  But is there a place for compassion when the sentencing is occurring----for society, to use an example, to respect the value of a killer's life rather than sentencing him to death?  If we're a "hang them high" sort of society, are we not brutal?  But then one could ask if anything less than the death penalty for murder is fair, in terms of the punishment fitting the crime.