"Dumbest" wouldn't be the word I'd use here, considering the views on immigration are sharply divided by education level. I reckon HN has an overrepresentation of people with (at least) a college degree, relative to the general population.
> Immigration on Hacker News is like the dumbest topic here.
Insert "We're All Trying To Find The Guy Who Did This" meme.
Personally, I care far more about the dehumanization of my fellow human beings than how open or closed the borders are.