Economists aren't exactly noted for their expertise in Cultural Studies (I think that's what I'm doing here), but I'm going to give it a go.
The fact that the Arthurian legend still resonates 1,500 years later tells us something about people, their hopes and fears. According to legend, Arthur was the British resistance leader who fought the invaders. His side eventually lost, which is why I am writing this post in English and not Cornish. And the Arthurian legend all begins with Vortigern's failed immigration policy. Vortigern invited some Saxons to settle in Brtain, and they invited other Saxons to join them. Which is why England exists. (It's ironic that the Arthurian legend is so popular among the descendants of his enemies.)
When economists disagree with public opinion, I normally agree with the economists. But we ought to think twice when this happens. Maybe, just maybe, public opinion is based not on ignorance but on something that our models leave out. When it comes to immigration policy, I think it is correct to say that elite opinion (which includes economists) in rich countries that are attractive to immigrants is generally more favourable to immigration than is public opinion. The elite finds public opinion a bit embarrassing, and tries to ignore it. They remind me of parents trying to get their kids to eat broccoli: "It's good for you, and you will like it once you get used to it".