Contradiction with Deuteronomy 20:16-17
These verses command the Israelites to completely destroy certain cities and leave no survivors, unlike the predicament in Judges 21:9 where Israelites are concerned about a lack of people.
Deuteronomy 20:16-17: But of the cities of these people, which the LORD thy God doth give thee [for] an inheritance, thou shalt save alive nothing that breatheth:
Contradiction with Exodus 20:13
This verse commands "Thou shalt not kill," contradicting the context of warfare and its consequences seen in Judges 21:9.
Exodus 20:13: Thou shalt not kill.
Contradiction with Matthew 5:44
Jesus instructs to love enemies and pray for persecutors, whereas Judges 21:9 reflects on the aftermath of conflict among tribes.
Matthew 5:44: But I say unto you, Love your enemies, bless them that curse you, do good to them that hate you, and pray for them which despitefully use you, and persecute you;
Contradiction with Romans 12:19
Instructs to not avenge or seek vengeance, contradicting the backdrop of war-related justice sought in Judges 21.
Romans 12:19: Dearly beloved, avenge not yourselves, but [rather] give place unto wrath: for it is written, Vengeance [is] mine; I will repay, saith the Lord.
Contradiction with Proverbs 24:17
Advises against rejoicing when an enemy falls, which contrasts with the outcomes of tribal vengeance in Judges 21.
Proverbs 24:17: Rejoice not when thine enemy falleth, and let not thine heart be glad when he stumbleth: