A tentpeg through his head - pure, lovely, and commendable?

Quite some time ago Mark Heath wrote a worship song with the following words:

Come hear the story of Deborah
And the defeat of Sisera
She prophesied, "take an army, and fight against Canaan"
The people gladly followed under Barak's command
And God gave the battle into their hands

There they fell, dead
God's enemies defeated
Killed by the armies of Yahweh
But their leader ran away

Blessed be Jael the Kenite
Who offered milk and a bed for the night
She took a tent peg in her left hand, and a hammer in her right
And when he started snoring, she approached him from behind
And crushed his skull with all of her might

There he fell, dead
With a tent peg through his head
Killed by a friend of the family
As he slept in her bed

Poor old Sisera's mummy
Wonders where her little boy has gone
"Now don't you worry, he'll be home soon"
"He's probably raping a girl or two"
"And when he's done with them he'll steal some clothes for you"

There he lay, dead
With a tent peg through his head
Killed by a friend of the family
As he slept in her bed

When I first heard it (and blogged about it) I was very unsure about it. I have listened to it a lot since then, and thought about it some more. I am convinced that we must begin to worship God for his judgment of evil people. When Habakkuk complains to God about injustice against the poor of Israel, God's response is to assure Habakkuk they the perpetrators of injustice will be punished and Habakkuk welcomes that. And Jesus did not do anything different, as Mary the mother of Jesus sings with joy to God:

He has shown strength with his arm;
he has scattered the proud in the thoughts of their hearts;
he has brought down the mighty from their thrones
and exalted those of humble estate;
he has filled the hungry with good things,
and the rich he has sent empty away.

I have to challenge myself to ask why I have trouble singing with Mary on this. I suspect it is because I am not the poor but the rich, and am aware enough of my sin to dislike the idea of coming judgment. Yet Jesus held out hope even to the rich in letting himself be judged and I must rejoice but with a humble heart.