A book that commands the extermination of entire peoples, like the Canaanites, cannot be a source of moral guidance.

Why people find it persuasive

The conquest texts (especially in Joshua and Deuteronomy) describe herem — devoted destruction — of towns including apparently noncombatants, in language that on its face reads as a command to commit what by any modern standard would be a war crime, and no degree of theological sophistication can make that comfortable to read.

Important distinctions

• • Description of ancient events vs. timeless universal moral prescription for all people in all times.
• • Literal, total, historically-verified extermination vs. stylized ancient Near Eastern conquest rhetoric (a documented literary convention).
• • A unique, non-repeatable act of covenant judgment vs. a general policy God intends believers to imitate.
• • Textual difficulty within a tradition vs. grounds for rejecting the tradition's moral content wholesale.

Christian response

• • Present the scholarly case (developed by scholars like Kenneth Kitchen, Paul Copan, and others) that herem language in Joshua uses conventional ancient Near Eastern hyperbolic conquest rhetoric — parallel language appears in other ancient inscriptions (like the Mesha Stele) describing total victories that archaeology and even the text's own later chapters show were not literally total, since Joshua itself later describes many of the supposedly annihilated peoples still present in the land.
• • Point out this is presented in the text as a unique episode of judgment tied to specific covenant conditions (explicitly framed, e.g. in Deuteronomy 9, not as ethnic superiority but as judgment on entrenched wickedness, with the same standard explicitly applied later to Israel itself when it commits comparable sin), rather than a general transferable ethic — and no biblical text commands or endorses anything like it as ongoing policy after this episode.
• • Note honestly that not all Christian scholars fully embrace the rhetorical-hyperbole reading; some (like Paul Copan in a different vein, or others taking a 'accommodation' or 'progressive revelation' approach) argue the text does describe real, if morally troubling, divine judgment analogous to other acts of judgment in Scripture (like the flood), and that its difficulty should be acknowledged rather than fully resolved away.
• • Distinguish the question of biblical inerrancy/interpretation debates from the practical ethical question: nothing in Christian ethics as taught by Jesus and the apostles treats these texts as license for religiously motivated violence today, and the church's mainstream moral tradition (just war theory, prohibitions on targeting noncombatants) developed in explicit tension with, not extension of, these narratives.
• • Acknowledge that this remains one of the texts most cited by former believers as a reason for leaving the faith, and that pretending there's a fully satisfying resolution understates the real difficulty; intellectual honesty here strengthens rather than weakens the overall case for taking Scripture seriously.

Christian counterresponse

Theologians who take this seriously (rather than dismissing it) generally argue from God's prerogative over life as its giver, analogous to (though far more troubling in scale than) death by other natural causes God permits, combined with the specific covenantal and typological role Israel's conquest narrative plays in the larger biblical story — while conceding this is one of the areas where confidence should be more modest than on, say, the resurrection.