I remember at one point encountering the Open Borders site, considering that it sounded like a pretty good idea, then reading through much of the site and becoming decreasingly convinced as I read the specific arguments, which consisted of more holes than solid points.

Recently, it's come up again, specifically in an interview with Caplan which was going around (I saw it via Kaj). Again, I was initially intrigued by the idea, but the more I saw of the actual arguments, the weaker they seemed. He seems to routinely deflect the significant concerns with non-denials and never actually address the pragmatic reasoning against it.

There are many counterarguments listed on the Open Borders site, and for that I give him credit. Especially as he actually attempts to engage with racialist arguments, rather than dismissing them.

I'm not sure if it's a technique worth crediting. There are voting trend issues with Hispanic immigrants that do not boil down to paranoid delusions about the Reconquista, and there are arguments regarding crime and immigration that are strongly and obviously distinguishable from sending every African-American person -- including those innocent of any crime -- out of the country. I'm hard-pressed to believe those arguments were selected for any reason but their weakness and unpalatability.

I personally favor reduced barriers to immigration (outside of a criminal background check and unique person identification, the modern limits are counterproductive at best), but writing up the worst arguments against that belief doesn't really strengthen them.