Beliefs and facts are often different and the beliefs usually control the facts. One example is higher education tenure.
Faculties really do believe the only protection that academic freedom has is tenure. In spite of other constitutional protections, faculties think tenure is more protective. A parallel case would be Title IX. Despite the fact that the Civil Rights Act of 1964 protected all people, including women and minorities, from employment discrimination (as well as other forms of discrimination), women were, nevertheless, not treated equally in higher education in numerous ways (employment, acceptance to graduate programs, etc). It took the very specific language of Title IX--implemented in 1972--to give women equal rights in higher education employment decisions and, most notably, in athletics.
Faculties see the constitution and other statutory protections as inadequate to assure academic freedom. Regardless of any and all other protection, faculty members believe that only tenure gives them full protection.
Remember that tenure creates a lifetime employment contract between the university and the professor which in reality cannot be terminated by the university.