@Corinthian’s post was certainly informative. But the scenarios are slightly different, as Gibson was a business serving Oberlin, whereas the adjunct was an employee of the college.
So I will ask a different question. What disparaging thing can a business publicly say about an employee and have it be protected free speech? For example, can a business publicly call someone a racist and then fire that person without repercussions? Or misogynist? Or unethical? Does the answer change if the vast majority disagree with the assessment of the business?