Honesty is generally too much to expect from this administration, but this is a case where it would be useful for everyone if the Trump White House just admitted that this policy was conceived as a deterrent — traumatizing a certain number of families in the hopes of bringing greater order to the border in the long run.
That admission would get us closer to the hard problem in migration policy. Some harshness, some deterrence, really is unavoidable in any immigration system that doesn’t simply dissolve borders. So policymakers are therefore obliged to choose tolerable cruelties over the intolerable one that we’re witnessing in action right now.
This dilemma was apparent (or should have been) in the Obama years, when a far more pro-immigration administration pursued sweeping amnesties, eventually by executive fiat. Liberals hailed those amnesties while paying less attention to the consequences of the Dreamer amnesty in particular: It created the impression that kids brought to the United States illegally would soon gain legal status, which in turn helped drive a surge in children being sent north without their parents, overwhelming the Border Patrol and saddling the Obama White House with a problem that it ultimately passed along to President Trump.