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.
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).
