The problem is, there seems to be increasingly a dichotomy (rather than a spectrum) between wall-building anti-immigration and completely open borders "nobody is illegal" pro-immigration opinions.

The centre-right and centre-left politicians in Europe and the US have failed to make the case for any kind of sensible level of immigration, and rightly or wrongly the electorate in more or less every nation does not want uncontrolled mass immigration.

In a world where the Conservatives say "we will get net migration down below 100,000" and then deliver net migration >700,000, you can see why more extreme controls on immigration seem appealing (to an electorate that does not like mass immigration).