You're confusing "free speech" with employment.    If you own a company - do you actually believe that "free speech" covers an employee using company resources to author an internal memo that has nothing to do with his job?     If you do, you're mistaken.    Companies have every right to set policy.    If you don't like these policies, then you're free to leave.     

His "free speech" hasn't been impinged.    He was fired.    Although it's easy to relate the two - they really have little to do with one another.