If the ethics of the work in the professional work area is unmoral and completely wrong, there should be no right for the employer to fire in such ways due to disadvantages done by the employers itself. If the services provided within the company is completely unfair and the treatment and services the customer receives back is known to be unnecessary. There is a right for the employee of the company to take action in such decisions and the company to make wise consideration in what the employee has to say.
Yes, employees should not have their complaints silenced for fear of losing their jobs. Not only does the First Amendment to the U.S. Constitution protect the right to free speech, but the employee is in the best position to know when a company could be doing better. Employee complaints, when handled in a tactful, constructive manner, should be valued by their employers as a means of improving the company.
Many of us decry the heartlessness of companies that engage in unscrupulous business practices. Whistleblowers help expose some of theses practices, which allow the public ammunition to help make a change. Employees know more than anyone else about the practices of these companies and if they are being told to do something they consider unethical, they should file a complaint.
If an employee is paying for services from their employer they should be able to make complaints without retaliation from the company. At the time of their complaint they should be treated like a customer, not an employee. Employees are allowed to make complaints about other employees work ethics. This should be no different.
The entire reason why you can't screw around on Facebook is because employers can legally check it and since you're mostly in at-will employment can legally release you from that employments based on what you're saying externally.
Also your question completely misrepresents the actual case due to the fact that the person was not fired from Comcast at all and the grounds for being fired had nothing to do with the complaint but instead policies and ethics which is based entirely on whether Comcast is lying about this person's behavior relating to the ethical nature of their conversations.