Thoughts on Reading Numbers 31

I was reading Numbers 31 the other day. At the LORD's command, Moses sends out the army of Israel to take vengeance on the Midianites. The men fight victoriously and kill every adult Midianite male (v. 7). As they return, Moses, the priests and the community leaders go out to meet the army and Moses becomes angry with them. At this point (vv 15-18) we hear the voice of Moses:

“Have you allowed all the women to live?” he asked them. “They are the ones who followed Balaam's advice and enticed the Israelites to be unfaithful to the LORD in the Peor incident, so that a plague struck the LORD's people. Now kill all the boys. And kill every woman who has slept with a man, but save for yourselves every girl who has never slept with a man.”

These verses really trouble me. I do not know how to reconcile them with God being a God of love, mercy and grace. Through his prophet Moses he is ordering the murder of women and male children and sanctioning the enslavement of female youth and children. This ostensibly is being done because the women led the Israelite men into idolatry. But even if we acknowledge that some of them did this, a blanket judgment on all the older women seems quite harsh. And what became of the young women who were kept alive? Were they mere household slaves, which would be bad enough, or did they suffer even worse abuse and degradation? The text is vague about this other than that a certain percentage of them were offered to the Levites as a tribute to the LORD.

Considering how readily we condemn Islam for inciting acts of violence against non-believers, it seems we need first to wrestle with the skeletons in our own closet. I read a book entitled Laying Down the Sword that raised this question and gave some suggestions for how one needs to deal with such passages, as I talked about here. I'd like to find a hermeneutic that gives me a means to interpret and respond to passages like this. Currently, along with Rachel HeldEvans and many others, I'm reading N.T. Wright's book Scripture and the Authority of God. I'm hoping that he may point to a way forward through passages like this, but we haven't read far enough in the book to have an answer yet.

I think these passages should disturb us. The commentary in my NIV Study Bible (2011 edition) doesn't indicate that these passages are in any way disturbing. This violence is treated as the appropriate and reasonable response to the godlessness and idolatrous ways of the Midianites, particularly their acts in leading the Israelites astray. Is it as simple as that? If so, why do we not pursue a similar course of vengeance today when we see acts of godlessness? (Mind you, I'm not encouraging this and would be appalled by anyone who did encourage or act in such a way.) These are some of the questions asked by the author of Laying Down the Sword. Unfortunately I've heard little or no dialog about these issues in most Christian circles.

How do you respond to this passage? How do you reconcile this with a God of love, who desires that all may be saved? What do you think should be done with such violent passages?