In ancient Israel, the Israelites had Cannanite, Edomite, and Midain concubines. So why is it wrong now?
Because in ancient times there was no PLO, Hamas, Arab nation, Islam.
And most importantly, there was no such thing as a sense of national identity.
There were tribes, not nations. If you won in a war, you would take a complete and a long-term control over the defeated tribe and/or territory.
Woman were rightless and obeyed any fate. Men had a choice of either fighting or cooperating.
Now, if you defeat one arab country, the population of this country will know that they have a back up from a) other Arab nations and b) Muslim nations.
Thus the Arab women will be still loyal to the ideals of Islam and PLO.