Yeah ...... uh .... huh? I thought my point was that cultures aren't all the same.
Let's run it back again:
"Immigration should be allocated on a limited basis to ONLY
those cultures who have a track record of assimilating into Western values."
Not to people -- to entire cultures.
In order for this to work
everyone in a given culture would have to reflect that culture's values, IOW it would have to be monolithic. Someone from Culture X that does not "have a track record of assimilating" (whatever that might mean, in whose opinion?) is denied even though it's his earnest desire to assimilate, while somebody else from Culture Y that does have such a "record" but is actually coming here to poison the water, we throw the doors wide open for him.
Now if I'm a "death to America" terrorist planning to plant a sleeper, I'm recruiting one from Culture Y.
In the real world cultures are not monolithic; its inhabitants are diverse. This is where blanket generalizations lead.