I don't like it. I don't agree with it. However, it absolutely is both free speech and protected speech. This of course does not mean it is without consequences.
Every job I've ever seen has included the proverbial "Line 13" in the job description: "Other duties as assigned". The joker that did this, were I his manager, would find himself working with the groundskeepers or in the dishroom or somewhere equally repulsive to him (in short, anywhere he had no access to a computer or the public, and where any destructive misdeeds would be "destruction of government property".) He would also find, if I could do it legally, that his salary was reduced commensurate to his duties and his lackluster performance thereof. Finally, when he decided enough was enough and was ready to walk off the job, his job file would be permanently marked that he left without proper notice (if true) and that he was a "never rehire".
Try getting another job after that, bandana-face.
Blessings,
Bill
Where ya been Bill? Great to have you back.