Immigration and the Economy

I'm pretty sure none of what I'm saying here is ground breaking, but I'm surprised people don't talk about this more often.

It seems to me that economies are built from the ground up.  So, you need tons of minimum wage workers, then you need a lots of trade workers, and then some specialized technical workers, and then a very few executive type workers.  I know I'm oversimplifying here, but the point is that you need to make sure your base is solid or the rest of the pyramid will not fill out.
What I see in the US historically is that there has always been a healthy level of immigration to our country, whether that is legal or illegal.  This immigration produces a large number of minimum wage workers that help support our economy.  I think that because of this historical immigration, the US economy has always been one of the strongest in the world.  The funny thing is, that as soon as the economy shows signs of weakness, the government goes after illegal immigrants and tries to deport as many as possible to theoretically improve the job market for US employees.  My theory is that many of the people who are deported are not actually replaced and overall, this hurts our economy.  In addition, when economies are down, it's not the minimum wage jobs that we really care about, it's the trade jobs and specialized technical jobs that are most important to us.