What was Marx's view on immigration? I'm still new to socialism (have only read the Communist Manifesto), so my knowledge is fairly limited. I've heard some Alt-Right people on Twitter use the phrase "reserve army of labor" (which I believe Marx coined) in relation to illegal immigration, implying that Marx would not support the modern left's position on this issue. Is this correct? Or are they misunderstanding things?
As I understand it, the economic argument against illegal immigration is that it lowers wages, but businesses aren't hiring illegal immigrants out of a preference for duskier workers. They're hiring them because illegal immigrants are typically desperate and have few job opportunities available to them. Therefore, businesses can get away with paying them under the table at below minimum wage rates. Desperate, financially insecure native born workers serve the same function and may even be preferred due to fluency with English, but there just happen to be many more Mexican workers who fit this bill than Americans. As a result, they tend to be the scapegoat for this issue. Presumably for socialists, the source of the problem isn't immigration. It's capitalism and the system of wage slavery. But even in the short term, wouldn't this be better solved by forcing businesses to keep logs of workers on their payroll, how much they're paid, etc., and imposing strict penalties on businesses that try to circumvent labor laws, rather than focusing on immigration restriction, which only addresses the issue superficially if at all?