How many immigrants can we realistically take in?

I understand that most immigrants are people who are simply hoping for a better life. I’m the product of immigrants who were hoping for a better life in America.

At the same time, I’m sure that the majority of the world’s population desires a “better life”. Most of the world’s countries are poor. Most are far less developed than Europe/America. But that doesn’t mean we can just let everyone who wants a better life come to Europe/America. And is it really a better life if those immigrants just end up in gangs and ghettos here? Not all do, of course, but some do (including people I know), and that’s pretty tragic.

It’s also sad to me that it seems these countries with problems are giving up. They’re admitting they can’t fix the problems, so they’re just saying “let’s all come to Europe/America”. But that’s not a long-term solution. And what does it say of the people left behind?

I’m interested in a more in-depth discussion about the long-term ramifications of immigration. I want to know how tenable it is.