Not as many as you think. Have you been to Western Europe?
I am well aware of the prevailing attitude toward the US, but to me a sensible number of immigrants would be in the low 10’s of thousands. You don’t think there are that number of Europeans who would have wanted to escape the socialist Europe in the 60’s and 70’s? Of course, the attraction is less now, but I am thinking more of the immigration policy we could have had, not the one Ted Kennedy stuck us with in 1965.