Peter wrote:

I thought that in the U.S. and U.K., anyone can take any job they
can get hired for, at any wage and benefits that they can negotiate.

Uh, no, not by a long-shot.

First, you have minimum-wage laws and all sorts of nanny-state
workplace rules. Then there are unions. Next is government licensing
and permitting for many occupations. Some jobs are intrinsically
illegal! On and on.
How does that change the basic fact that anyone in the U.S. can take
any job they can get hired for? You are arguing that the hiring
playing field is not level. That's a completely different issue. Bottom
line, you are free to change jobs to any job an employer is
willing to pay you to do. Restrictions on the employer's hiring
choices is a different subject entirely. Stop changing the subject
every time someone catches an inaccuracy (or worse) in what you say!

No, restrictions on the employer interfere with the negotiations.

Further, the restrictions apply to the applicant also. For example, an
applicant cannot demand to being paid less than the minimum wage or insist
on not wearing the government-mandated safety helmet.