I'm not certain Matt wants to base his arguments against a guest worker program solely on grounds of income. After all, the bottom fifth of this country never saw greater gains than in the immediate post-war period -- exactly the era when the Bracero guest worker program was in place.
Which is to say, as we already know, that immigrants generally -- and 200,000 person guest worker programs specifically -- have very small downward effects on on native wages -- if indeed they have effects at all. In large part, their jobs are complementary to, rather than competitive against, native worker's jobs. And they both create and keep wealth, jobs, and industry in the country. If the migrants weren't coming over the border to pick strawberries, it would be the strawberries coming over the border instead. The margins are low enough, and the product mobile enough, that it'll just get outsourced.
In that way, the importation of low-wage labor often isn't zero-sum; it sustains industries that would either leave the country or disappear in the absence of such labor. Indeed, Matt made this point eloquently in a post I came across while Googling the other day. "There aren't any jobs Americans won't do," he wrote, "but there are plenty of jobs that won't get done at the prices people are willing to pay...There's a cheap Chinese takeout place on my corner owned and staffed by immigrants who, I assume, don't get paid very much. There's no reason in principle why a native-born American couldn't learn to work a wok and become a short-order cook at a Chinese restaurant. In practice, though, that kind of thing doesn't happen. Cities without Chinese immigrants don't have Chinese restaurants." That was a smart point, one that he seems to have forgotten.