Question

A valid counterargument to the statement that immigrants cost Americans jobs is that

Answer 1

Immigrants are willing to do the jobs that Americans won't
do, for wages that American's would not accept.  They take
the jobs that Americans don't want.

Answer 2

I believe the answer is:   one-fourth of all new businesses are started by immigrants

For example, Google, which arguably the largest tech company in the world today, was co-founded by a russian Immigrant named Sergey Brin.  People in some media like to focus on how immigrants affect the availability of  low-skilled labour because it most likely give the most support from the supporters of a certain political party.