The oath that the Israelites mentioned in Judges 21:5 required them to put to death all who did not come to the assembly. So should they not have also put to death the virgins? What would be the basis for their applying the oath selectively instead of absolutely to Jabesh-gilead? There is no such principled basis. Rather, the Israelites are operating out of empty morals. They simply want Benjamin to survive, by any means necessary.1
12 And they found among the inhabitants of Jabesh-gilead 400 young virgins who had not known a man by lying with him, and they brought them to the camp at Shiloh, which is in the land of Canaan.