It does apply to technology. My point isn't "some people get hurt, therefore open borders are bad". Some people are hurt by technology, but the net benefits are so great that it's generally worthwhile. I think the tradeoff is a little closer to even for open borders.
Thinking about it some more, it seems there are three main effects:
1) High skill effect. If you invite someone who has higher productivity than average for your country, that has basically the same effect as technology. This is a strong argument for skilled immigration.
2) Low wage effect. If you invite someone who's willing to work for a lower wage (being from a poor country), you are better off, but only until they learn to ask the same wage as natives. This is why I think Caplan's main argument for unskilled immigration is weak.
3) Poor proximity effect. Most natives don't want to live among poor people, so natives become worse off when you invite poor immigrants. This is a strong argument against unskilled immigration.
