What jobs? Where are these jobs?

The point that you are missing is that most of these illegal immigrants are already working in jobs that "local" people are not interested in.

Making these immigrants legal has a number of advantages. For instance, they (and their employers) will be contributing taxes to the economy. There will be less exploitation in terms of poor working conditions and undercutting of minimum wage legislation if these workers have the protection of the law. That's good news for other workers because it means that employers can't use the cheapness of illegal immigrant workers to put "local" people (who have to be paid properly) out of jobs

There is also the law enforcement aspect. At the minute, enforcing immigration law is very hard, and often fairly pointless. Most of the people who get "caught" are hard-working people who are actually very socially and civically minded - real contributors to American society while the "problem" people get missed. That law enforcement time and money would be better spent elsewhere