Treating the employee as an end in itself means, at the least, giving reasons for a firing. 2. Employers and employees should be free to enter into contracts voluntarily. The employer's freedom to hire and fire is balanced by the employee's freedom to accept employment and quit. Any departure from Employment at Will would harm the efficiency of business, and the resulting extra costs would ultimately be passed on to employees. But employees are not given the option of choosing due process vs. extra pay.
Due process requires the same giving of reasons that is required of all other management decisions.
Regulating employment contracts requires government intervention and undermines the free market. The distinction between public and private spheres must be maintained. But the distinction is no longer a clear one. Private property is maintained by public power. Public and private institutions sometimes serve the same functions.