See here for the website of a leftist organization that wants to stop immigration in order to help the environment and the poor. This organization is a holdover from an earlier era, but unlike the other leftists it hasn’t changed its stance on immigration. It was vilified recently by the Southern Poverty Law Center, according to this post by Steve Sailer (hat tip: Mark Spahn). I usually remember changes the left has gone through, but I had forgotten about this one. See also this essay by Ron Unz that was published nearly twenty years ago. It seems that, at least in California, right and left back then were switched around on the topic of immigration, with the right supporting the new immigrants because they saw them as on the right (opposed to abortion, etc.), while the left saw them as destroying their attempts at slow growth.
The left’s support for immigrants, whether from Mexico or the Middle East, is in a way insane because it means either a lot of conservative Catholics or a lot of conservative Muslims will be allowed entry into our country. The left, apparently, loves conservatives, as long as they are foreign. Is this because they expect them to turn into leftists? Well, no, because it would be racist to force them to assimilate, and without any pressure, there is no reason for them to change, so they will stay conservative. Presumably, the day will come when the left realizes it has made a big mistake.