No civilized society and social contract can survive unless violent crimes are punished with extreme prejudice, and human rights are protected, which includes punishing violations of them. In just one single village, 7,000 Yazidi women were enslaved and raped, and their menfolk and children killed. Only their bones remain. Anyone voluntarily joining a group that committed such ultraviolence in the name of religion breaks her bonds with civilized society and humanity itself. They cannot just waltz back, nor should they be allowed to.
It is abhorrent for their fellow citizens, who are decent and contributing to society; it is unjust to the Syrians and Kurds and Yazidis, upon whom the darkest crimes of humanity were unleashed and who rightfully seek justice and retribution; it is treasonous to the land beneath their feet; and it denigrates the minorities who are law-abiding, hardworking, and have made the West their home. Not everyone deserves another chance. Nor should they get one, if one intends to see Western civilization preserved.