One idea: that they bring capital with them.

Increasing the supply of labor while not increasing the supply of capital can drive down productivity and wages in the nation getting migrants. If they come with accompanying capital, it could help maintain or improve productivity.

I was basically pointing out that WSJ is biased towards loose immigration and to take the article with a grain of salt. I favor legal, limited, and controlled immigration. Immigration en masse of poor, low skilled labor to a developed country like the US (where manufacturing is on the wane) is not a net benefit in the long run.