It's a load of bollocks anyway, if you're fleeing a warzone or persecution you might not have the time to get all your legal affairs in perfect order so you can become the model refugee and meet the standards of the racists who will just find another excuse. You want people to stop coming here? Maybe look at the root causes.Y'know this whole business of "they're destroying their documents on the flight in to the country, we don't know who they are?"
Presumably the people in this scenario had to have documents to get on to the plane.
So there's a reasonable chance of knowing who they are, the passenger manifest would be available to the authorities.
I don't know how many people might or might not be doing this and how many might be on a particular flight, but it can be narrowed down to a small group.
Not Ukraine related but read this recently,
My Fourth Time, We Drowned by Sally Hayden: 9781685890575 | PenguinRandomHouse.com: Books
Grim stuff, she doesn't go much into the world politics stuff of it all, but we're all complicit in endless crimes against humanity. No one is coming here when things are great back home.