One of my fantasies is of a classroom in which a tenured economics professor at an accredited institution of higher learning says, "We must have free trade," and a few students leap out of their chairs and shout, "You first!"
I don't know of any student who has stood up and said it. But a few years ago, when I, a tenured professor, was laying out the benefits of free trade, a question a student asked led me to think that he was asking something like that but wasn't quite willing to come out and say it, on the mistaken impression that I would be offended. So I introduced the thought immediately. I was teaching a distance learning class and I pointed out that that could just as easily be done from, say, Singapore and at probably half the price. So that's not quite immigration. But I also pointed out that I wanted the U.S. government to allow in people from other countries who would compete with me. I still do.
Moreover, I used to think, like Arnold, that it is hard for a professor to immigrate to America. I based that too much on my own tough experience with the INS in the 1970s when I immigrated from Canada. Arnold is right that there is not free immigration of professors. My impression from a previous post by Bryan Caplan, though, that I can't find offhand, is that immigration of academics to the United States is much freer than of people in most other kinds of jobs.