Deuteronomy 20:18

that they may not teach you to do according to all their abominable practices that they have done for their gods , and so you sin against the Lord your God .

Otherwise, they will teach you to follow all the detestable things they do in worshiping their gods, and you will sin against the Lord your God.

That they teach you not to do after all their abominations, which they have done unto their gods; so should ye sin against the Lord your God.