Why At-Will Employment is Bad for Employers
Most employers believe that if they set up an at-will system and police it vigorously they will be safe from lawsuits. However, despite almost universal acceptance of at-will relationships in the United States, employment litigation is on the rise and is now a large percentage of cases on court dockets. A recent article by Ellen Dannin gives thoughtful consideration to the at-will doctrine and whether it still serves a useful purpose.
In her article, she notes that dissatisfaction with at-will doctrine has led courts and legislatures to develop many common law contract, tort doctrines and statutory exceptions, leading to greater complexity and uncertainty. By now most bad reasons for firing workers have been made illegal, so an at-will regime is limited to firing workers for a good reason or no reason. It also seems unlikely that most employers want to fire their employees for no reason, because, by definition, this means firing good employees. Thus the so-called "at will" doctrine is reduced to one in name only. Her article asks what is the benefit to employers of this strategy. . . and what is the alternative.
Source: LaborProf Blog
The main reason for maintaing employment at will is the burden of proof. True there are many exceptions to employment at will, but the employee bears the burden of proof in establishing them. If employments could only be terminated for cause, the employer would have the burden. You can debate just how important burden of proof is, but it's always better for it to be on the other side.