The evilness of bible heroes...
In the book of Numbers Moses had given instructions as to how to treat Midianite captives. Essentially, everyone was to be executed except virgins, whom the victors were allowed to keep alive for themselves. God then gave instructions as to how the booty, including 32,000 virgins, should be divided up between the victors. Summarised the relevant biblical passage: "Here is an order to butcher the boys, to massacre the mothers, and debauch the daughters".
The virgins had been spared for any immoral purpose or they were spared so that they could be taken into slavery. Obviously, there could be no ethical objection to this, since slavery was divinely sanctioned. The latter reason was perfectly acceptable to mainstream Christians, who found sex objectionable but slavery not at all objectionable. According to the Churches, slavery was not merely permitted, it was obligatory. Slavery was a God-given institution. To oppose what God had sanctioned was positively sinful.