And where did the Church Fathers teach or endorse this suicidal inversion of Christian charity?
Nowhere I've read... and I've read a lot of them.
Take John Chrysostom, one of the towering Fathers of historic Christianity.
Commenting on Romans 13, Chrysostom taught that civil government exists precisely because human society requires order, peace, restraint of wrongdoing, and protection of the weak from the powerful.
Without civil authority, he warns over and over, the strong would simply prey upon the weak.
Government, in his understanding, is not commanded by Christ to stand aside while chaos consumes the people entrusted to it.
He wrote that its very purpose includes repelling enemies/invaders, suppressing sedition, restraining disorder, preserving peace, protecting the public and safeguarding what belongs to them. (Exactly the opposite of what's going on in the West right now; a complete INVERSION from hell for all to see.)
In Homily 6 on First Timothy, discussing rulers and military protection, Chrysostom says their safety provides security to the people and describes rulers as “bulwarks thrown up before us” so that those inside can live “in peace and safety.”
So imagine walking up to John Chrysostom and telling him:
“Actually, John, Christian rulers must knowingly not protect their borders and permit a dangerous and hostile population to overwhelm their country, terrorize the innocent, destroy churches, exhaust public resources, and destabilize civil society; because stopping it would make Jesus angry.”
He would not recognize that as some advanced form of Christian compassion.
It turns his understanding of Romans 13 upside down.
Chrysostom preached radical charity toward the poor and stranger.
But he was not insane.
The people pushing this suicidal empathy can’t establish most of it from Christ, the apostles, or the early Church. They just take “love the stranger”, attach a whole modern political program to it, and then announce that rejecting the program means "rejecting Jesus".
Love of the stranger never meant abandoning your own children, families, and neighbors to chaos & danger.
If your “mercy” toward the stranger requires the innocent behind you to bleed for it, you have stopped describing mercy.