Why do we need all these illegals? What jobs will they take?

I am thinking about why tptb would allow hundreds of thousands of illegals in our country while paying people to stay home and while businesses suffer from lack of employees.

I need some help figuring this out.

If we take it as a microcosm you have one business owner whose two employees are now sitting at home making enough money they won’t work. So Joe is having to reduce hours. Meanwhile five homeless illegals apply for jobs. So Joe hires two non English speaking people to cook or whatever. What happens to the two girls he layed off when the illegals have taken their jobs?

Do the girls just stay at home forever?

Who pays into social security and into our tax systems if you multiply this situation times a million?

Please comment as to how you think this is working. I cannot figure it out.