I think XO has a point. You just can't realistically expect that an open border wouldn't create a lot of economic disruption in the job market. The wealthy, self-supporting Mexicans aren't the ones who will flock in. The poor will, and they'll ultimately create a huge drain on the health-care and educational systems, as well as on roads, police, sanitation, etc. Not because they are Mexicans but just because they are human beings. I just don't believe that their tax-paying contributions will come anywhere near making up the difference, certainly not in the short term. I don't know of any economic study that indicates otherwise.
However, I think that there are ways to cope with the influx, which appears to be unstoppable in any event. One is to cut the enormous waste of fiscal resources that is going into the military and the Middle East - - the cost of the Iraqi War and the annual subsidies to Egypt and Israel for starters. Secondly is to begin to seriously tax the rich - - they have obscenely more than any human being could seriously require for thousands of lifetimes and the time is long past due when this imbalance should be rectified.
The benefits of the influx are a bigger population. Ever see the ads that say "Our people are our most important asset?" I believe in people! I think they're a great asset. Anyone who doubts this should look at China. Wouldn't you like to have an internal market of that size? A labour pool of that size? Where's the downside?
People who live in fear of their own shadow see "criminals!" and worse yet, "terrorists!" in every foreign face. I would say, the U.S.A. already has one of the highest violent crime rates in the industrialized world. The contributions that the Mexicans can make to this problem shouldn't be significant. Besides, wouldn't a lot of Mexican criminals want to stay home, where they can bribe the cops, judges and jailers, terrorize the citizens and generally lead a much more comfortable life than they would enjoy under American law enforcement? And terrorists? Give me a break, please. They are already here and if they're not, they know how to get here. Getting in is probably the easiest part of their job, so don't rely on immigration as a front line of protection from terrorism. I'd concentrate more on airport and building security.