The greatest strength of the Republic has been, and always will be, it's openness. ANYBODY can come here, take a citizenship class, and become an American. Argue the melting pot versus the salad all you want--we are capable and flexible enough to allow for multiple ethnicities and sub-cultures, and yet this does not change America for the worse. (Except for the rabid isolationists, but they'll gripe about anything) Freedom and justice for all, remember?
Contrary to the complaining and whining of some folks who can't stand the thought of admitting that there are non-white, non-European, non-Christian citizens, they do exist, and they are important. It is the immigrant who keeps us strong and vibrant, whose cultural contributions make us more diverse and fascinating.
Immigration is a good thing. It always has been: the benefits have outweighed the costs, which have almost never been as horrible as some people want to think.
Now, that said...illegal immigration is still illegal, and is a major concern. Thanks to the heated rhetoric of a few citizens *cough*Buchanan*cough* it has become very difficult to calmly and carefully discuss the issue without accusations of 'appeasement' going one way and 'racist' going the other.
Obviously, we don't want just anybody coming in, or sneaking over the border for who knows what nefarious purposes. So we have quotas and limits. But the result? Legally immigrating is time consuming, costly, and a bureaucratic pain in the neck. Which in many ways encourages illegal immigration.
There's got to be a better way. I don't know what it is, but there's got to be one. How does one punish the guilty without in some way also punishing the innocent? That takes a form of wisdom that's in short supply these days.