This is a perniciously xenophobic take, tbh. Who are you to decide your values are objectively better than theirs? /s

There is a village A dragon comes to the village every year. In exchange for 2% of the children, it spares the rest and promises its “magical” protection from unseen enemies. This arrangement has lasted 2,000 years. Most villagers worship it, even though the custom has left their village far worse off than others in the land.

Some villagers move away. Not all of them are dragon-worshippers, but some are and they still try to summon the dragon.

Now the dragon free villagers face a choice:

Keep them out. But that means some innocent children among them will die.

Let them in. Risk the cult spreading again inside the walls and possibly bringing the dragon back.

Go kill the dragon themselves. Accept substantial casualties including innocent dragon worshippers and some of their own people.

Killing the dragon would mean temporarily brutal treatment of the worshippers and the destruction of their culture, but it would spare future generations from an unbounded amount of suffering.

I'm really not sure what point you're making here. What is the "dragon" in irregular migration. What is the "village"?