Matthew Poole and continuators on Numbers 31:17

17 Now therefore, kill every male among the little ones , and kill every woman that hath known man , by lying with him.

Which they were forbidden to do to other people, Deut. 20. 14. except the Canaanites, to whom this people had equalled themselves by their horrid crimes, and therefore it is not strange, nor unjust, that God, the supream Lord of all mens lives, who as he gives them, so may take them away when he pleaseth, did equal them in the punishment.

Partly for punishment, because the guilt was general, and though some of them only did prostitute themselves to the Israelites, yet the rest made themselves accessary by their consent or concurrence or approbation; and partly, for prevention of the like mischief from such an adulterous generation.

Marginal references: Judg. 21. 11.; Hebr. a male.