I got your PM, but I also got an error message when I tried to reply to it. Our software can be pretty clunky sometimes. So, here's my answer:
The short answer is, because I'm a free market anarchist. I consider the freedom to travel a human right, not some right "granted" to us by a piece of paper.
A longer answer is, if we didn't want these people to come here, we shouldn't be effectively forcing them to come. Our War on Drugs makes it unsafe for them to stay where they're at, our welfare state pays them to come here, and our minimum wage laws force employers to hire them before they hire American teenagers.
A vibrant economy needs low-wage workers. When I was a kid back in the stone age, a lot of my friends got after-school jobs pumping gas and checking the oil for customers at gas stations. Still others got jobs bagging groceries, put the groceries into the cart, and then not only pushing the cart out to the customer's car or truck, but loading the groceries for the customer.
When was the last time you saw somebody do all that for you?
Those jobs are gone forever. So are jobs in textiles, in electronics manufacturing, everywhere. Corporate taxes are too high, minimum wage laws price U.S. manufacturers out of the market, and teenagers can't get jobs.
People say that "illegal" immigrants don't pay taxes. Well, of course they do. Even if they're paid in cash off the books, they still must pay sales taxes and excise taxes on everything they buy, and property taxes in their rent. Cities and states are broke already; take away these taxes, and even more of them will be declaring bankruptcy.
You don't see too many grocery stores, movie theaters, or any other businesses turning away "illegal" aliens, do you? Of course not. They depend on "illegal" aliens, too.
If you want to limit the number of Mexicans, Guatemalans, and Hondurans from crossing our borders, then building 50-foot fences or putting armies on the border isn't going to do it. Stop making laws that force them to come here, and force employers to "illegally" hire them.
And finally, if you disagree with me, don't worry. I'm pretty sure I'm the only person here with this opinion.
Onward and upward,
airforce