At will employment is really the crux that erodes all other possibilities of strong worker rights. In most European nations, firing employees functions on a sort of whitelist principle. You may not fire your employee except in one of this specific set of situations. This also puts a burden of proof on the company to demonstrate cause for dismissal. The situation in (most of) the US is more like a blacklist: all reasons for firing an employee are valid except for this specific set of situations. Now the burden of proof is on the employee, to show his situation was part of the blacklist.

If any (or) no reason for dismissal is a valid reason, it takes the tooth out of any worker's rights law you might seek to enforce. If you cause trouble for the company you can simply be fired (for "no reason" of course). Yes, that's technically illegal, and you can sue and/or contact the department of labor. They now have to investigate and find proof that you were fired for an illegal reason. Whether you get justice now depends on whether the department of labor is adequately funded, how good (expensive) your lawyer is, how well the company covered their tracks...

This is why many people in the US complain that "they have labor laws, the main problem is lack of enforcement!" The structure of the system is such that good enforcement is required for workers to benefit, but businesses benefit from bad enforcement.