This leads to a mismatch where, temporarily, employers can capture higher-skilled workers at lower costs.

Another comment, how are anti-disparagement clauses not a violation of first amendment rights?

This is a common misunderstanding of the first amendment. It's a short amendment, shorter than your comment, so you might as well just read the amendment.

First amendment applies to Congress (and after the 14th amendment, the state governments), not to any private citizen or organization. You're free to make private agreements that sign away any rights you have, except (after the 13th amendment) your freedom.

Immigrants arriving would benefit the economy (as long as they aren't too poor and take lots of welfare), at least ideally speaking.

> Why wouldn't it be fair for Americans to have an advantage in the American market place?

This is pointless, just like banning trade with X country to allow more jobs to be in America. It looks good on the surface, but really Americans would be losing out on the cheaper prices of X country's goods and services.

The key idea is that trades are mutually beneficial. When an employer hires an immigrant employee, they both gain.

Even if you wanted to specially protect American workers, it would still be more beneficial to allow anyone to take the job then use the excess GDP to make up for the lost wages of Americans. The estimate by Borjas (the most anti-immigrant economist) is that wages would drop at most 5% (IIRC) if open borders happened.