One advocate of immigration amnesty (I'm sorry; I don't have a link...going from memory) a while back said that the spread in cost from "enforcing" our current immigration rules and opening the borders is estimated at over a trillion dollars (I think over a 10 year period.) There should be checks and balances about who can legally come into this country, for sure. And, no system will be perfect; you'll always get "undesirables", whatever that means.

And as to the argument that they'll take away American jobs: as immigrants in past generations, they tend to do the jobs that American citizens do not want (farm jobs, heavy landscaping, etc).

*Gets out asbestos underwear*