I actually agree with your point there - if the employee wants the privilege of being able to quit at a moment's notice, they should also be willing to give up their employment protection. However, if the employee is willing to give notice, then there should be equal protection for the employee.

It's possible to arrange such things contractually.

Right, but my opinion is that the protection option should be the default, with employee (and employer!) free to negotiate a mutually beneficial agreement.

In my mind, it's a matter of inertia - if "protected" is default, then if an employer wishes to have the ability to fire anyone at will, they need to offer concessions - whether it be a higher salary, or the ability to quit at will, or whatever.

However, if "not protected" is the default case, then it becomes far more difficult for an employee to obtain such protection, as it's not beneficial to the employer. And as such, barring anyone who can negotiate their own contract (the minority, generally), most people will remain unprotected. And I believe that to be a problem, for reasons I mentioned elsewhere in this comment thread.

In many jurisdictions it's not possible (i.e., not enforceable in court) to sign away your statutory rights. This protects those with less power/resources (employees).

Equal protection would be severance equal to the advance notice period.

"""I like the idea of an employee being able to quit at a moment's notice, and that goes hand in hand with the ability of an employer to make the same choice."""

Not even remotely the same.

Because those two, worker and employer do not even remotely share the same power...

Agree. In a startup or a small business, the employer is the weakest. He/She must pay a high enough salary to get a competent worker, must pay for training, must pay salary while the worker is employed even if the company is not making money, must be aware and comply with labour regulations or risk a fine...

The employee just has to show up and do a barely acceptable job to get a steady pay.

Except that when you have a small company like mine. I have 3 employees. If anyone leaves it will hurt me as much as if I fire them.