[Rape and slavery justification in response to the following verse: Numbers 31:18. "But all the women children, that have not known a man by lying with him, keep alive for yourselves]

The Numbers passage you cite should be taken in context. Israel was directed to attack the Midianites because of their earlier misconduct with the men of Israel. Through the urging of the prophet Balaam, the Midianite women had been having sex with the Israelite men and led them into idolatry. Instead of destroying these adulterous women, the Israelite men captured the women and children, plus other spoils of battle.

Moses was angry that Israel had disobeyed God's commands and ordered them to execute these women who had caused Israel to sin against the Lord. The young girls were spared execution because they had not been involved in the adulterous sin. It was not that they were spared so that Israel could have committed sexual crimes with them. The New Bible Commentary says of the sparing of these girls that "they became part of the nation." There is nothing impure in this motive - simply an extension of God's grace.