@virvallis @Flick It's the received wisdom of the west having to be kind (there's that one again) to poor oppressed people from not-west, combined with a lot of people who think international conventions must be above everything else.
And then there's the "end of history" mindset, which also includes the belief that nation states are outdated relics and borders don't matter. This end of history idea became very popular at some point among the political and cultural elites, and they seem to see it as a fundamental truth.
The cherry on top is the "all cultures are just as good" moral relativism, that came about on the coat tails of postmodernism.
In short, I think it's an unfortunate coalescence of several cultural trends, as most things tend to be. If you look at the people advocating for this situation, you typically find they hold all or most of the above views. And if you look back at the last decades, you'll find those views floating up and becoming very popular among a certain crowd of people.
And then you had a few true believers in a few key positions, like Angela Merkel, who had enough power to push this approach in their fiefdoms, and enough influence to get others to adopt it too, and there's your poison.
And now you have Keir Starmer who no doubt happily carries the torch forward.