The argument against mass deportation is that it would be immoral and mean to kick out so many well meaning immigrants who came to America, often legally, to “start a better life.” Liberal Christians especially have been morally signalling against mass deportations on moral and spiritual grounds.
However, the situation is not that different from a more common one that just war proponents have been dealing with for centuries: is violence and force against an invading army justified, especially when many of the soldiers fighting for the enemy are simply “doing their duty” or forcibly drafted into fighting. For anyone but pacifists, the answer is “yes” violence is still acceptable despite the intentions of the individual members of an invading army.
It’s not difficult to extend this logic to our current situation. Immigrants are invaders whether they see themselves that way or not. They’re being used by hostile elite elements to overrun and destroy Western nations across the globe. The fact that some immigrants don’t recognize this doesn’t change the moral reality of what’s taking place.
Western nations must fight a just war to defend ourselves. The invasion has been more or less peaceable (with significant exceptions), and the Western defensive response can also be more or less peaceable if the hostile army cooperates. Immigrants invaded our lands, and we have the moral duty as defenders of our nations to deport them back to where they came from (or, at least, outside of our recognized national territory).