I think you have a valid point about the effects of our current immigration trends. We are getting the poor which are now needed to do the menial labor our economy requires, but if our economy continues to slow (as I expect) those laborers will be less needed and less welcome - especially the illegal aliens.
What worries me most is that after exporting much of our manufacturing base and jobs overseas, we are now beginning to see the same trends start in the service sector where jobs are moving overseas at an increasing rate. That is going to make any recovery from the recession even more difficult and will hit right at the heart of the middle class. If we are to revitalize the consumer so he can spend, he must have a job producing some kind of good or service in order to earn a good living wage - the more jobs that are exported to foreign economies, the fewer jobs are available to meet that need.