[Platapus]

Guillen had the right to say what he did.
The citizens of FL had the right to say what they did
The owners of the team had the right to do what they did

Florida is an "at will employment" state. There are only three exclusions in Florida's "at will employment" status. Florida statutes Title 31 state

448.102***8195;Prohibitions.—An employer may not take any retaliatory personnel action against an employee because the employee has1)***8195;Disclosed, or threatened to disclose, to any appropriate governmental agency, under oath, in writing, an activity, policy, or practice of the employer that is in violation of a law, rule, or regulation. However, this subsection does not apply unless the employee has, in writing, brought the activity, policy, or practice to the attention of a supervisor or the employer and has afforded the employer a reasonable opportunity to correct the activity, policy, or practice.
(2)***8195;Provided information to, or testified before, any appropriate governmental agency, person, or entity conducting an investigation, hearing, or inquiry into an alleged violation of a law, rule, or regulation by the employer.
(3)***8195;Objected to, or refused to participate in, any activity, policy, or practice of the employer which is in violation of a law, rule, or regulation.
History.—s. 5, ch. 91-285.

Even though I disagree with the firing, it is legal.