This betrays an incorrect understanding of how Christians understand Biblical ethics. Christians regard the whole Bible as inspired and infallible, and consistent with itself. That is the starting axiom. if we want to ask the question of whether genocide is allowed within Christian morality, then we have to look at the teachings of the Bible in both the Old and New Testaments. In the New Testament:
- Jesus’ Beatitudes blesses those who are meek and merciful (Matthew 5:2-11).
- Jesus proclaims that not only murder, but even hatred towards one’s brother is just as bad as murder (Matthew 5:21-16).
- Jesus commands us not to retaliate and to love our enemies (Matthew 5:38-48).
- In the parable of the unforgiving servant, Jesus teaches that those who do not forgive will not be forgiven (Matthew 18:21-35).
- Christians are commanded to be like Jesus. Throughout all the gospels, Jesus never engages in physical violence even against his harshest critics, the Pharisees who are always obstructing him. The only exception is when Jesus cleanses the Temple (Matthew 21:12-17, John 2:13-22) to drive out those who are profiting from religion.
- Paul writes that the fruits of the Spirit are love, joy, peace, forbearance, kindness, goodness, faithfulness, gentleness and self-control (Gal. 5:22-23).
With this in mind, now we turn to the Old Testament. In the Ten Commandments, God clearly commands the Israelites not to murder (Exodus 20:13). So what do we make of his commands to Israel to destroy and exterminate the Canaanites? We have to look at those commands in context. God was using the Israelites for a specific mission: to punish the idolatrous Canaanites, who worshiped other gods and practiced child sacrifice. In the same way, God would also use the Babylonians and Persians to punish the Israelites later when they were also disobedient to God’s commands. The Israelites were on a specific, limited mission which certainly does not apply to anyone living today, who is living in the age of the New Testament, where Jesus has fulfilled the law.
To summarize, based on this mini-systematic study of the Bible on the topic of genocide, we see that there are many commands in the Bible which urge love, mercy, meekness, forgiveness, restraint, and forbidding murder, which clearly point towards forbidding genocide. This is not a matter of picking and choosing different the parts of the Bible randomly, but deciding what the Bible teaches based on careful, reasoned, systematic study of the entire Bible, which we hold to be authoritative as a whole for faith and practice.