Once again (Don't you love how I always post the same thing
), most of the issues with immigration aren't that we can't benefit from people wanted to live and work here, it's due to the entitlements granted by living here.
The only real concern for screening the border might be to at least keep out known criminals but I think an open border policy could work fine .... once we've made changes elsewhere in the system.
We all enjoy a lot of free services - police, fire, freeways, medical (yes, you can free medical services if you know how), schools, libraries, legal protections, welfare and social services, low income housing etc.
All of these forms of assistance have costs. When we give them away too freely, we end up paying other ways (freeway congestion, if too many vehicles are on the road, hospital closures if it must provide too many free services, higher taxes for education, libraries, police, fire and courts etc.)
So, the main issue isn't that people want to come and live here and work. It's that we have a system that benefits the lower classes in many ways in comparison to other countries and this causes a pressure to come here.
I know need some of these services, and some of them need to remain free of cost (especially police and legal protections) but placing a small army on the border to keep people out, then giving them free services when they come is a rather schitzo view.
If someone came to America, worked and paid for their costs and didn't abuse public services, it's not a probalem and is actually a benefit to the U.S. We need more people like that :) If someone works in construction to earn money to buy a home from you, it's not an invasion ... they built a house or two elsewhere for you to take the money and live somewhere else if you wanted.
Anyway, I believe if we reformed much of the social services and possibly moved some government services to at least be partly fee based, we'd remove a lot of the abuse of these "free" services. This would lessen the burden on taxpayers and our infrastucture and provide a market in which private individuals could compete (you can't compete with a free government service, so no industries grow to supply more of that product).
It's likely this could reduce much of the flow of immigration, as well as lower the burdens of it to people already here. It could even provide a gain, as people with more resources and possibly skills, able to provide for themselves, would still find it possible to come.
We could still screen the borders to help reduce criminal elements that might try to enter the country but we wouldn't need a massive border patrol to try to keep everyone out because we'd have fewer immigrants, and those that came wouldn't be such an issue politically either.