If it was writ large across the sky and a glowing Angel was beseaching you and God's voice was in your ear saying "kill the rotten little sinner" and you were crying at the immorality "wrought upon you" and your hopelessly undisciplined brothers ....STILL I would say that after committing such an act of child murder, it would be YOU that deserved to have your throat cut.<quoted text>
Your post reveals a degree of correct understanding of principle. For humans, only killing sanctioned by God is justified. The killing of the Midianites was commanded by God, thus meeting your criterion.
Stop defending the indefensible.