You don't seem to understand what is required of whom. Corporations are required to act in the best interests of their shareholders (within the bounds of the law) or the shareholders can sue the company.

People are not legally required to do anything but they will be fired if they don't. If someone says something that makes a company look bad to their customers, they kinda need to be fired. Otherwise keeping them on may be detrimental to the interests of the investors.

Basically, you can say what you want but anything but positive attention may get you fired.