The supreme court has historically taken a more nuanced stance on this sort of issue than you.
Broadly speaking in the US everyone has many constitutional protections against the government restricting them in certain ways. When you become a government employee you give up only the most narrow subset of the protections necessary for the government to effectively be your boss.
This means the professors have a reasonably strong court case as mentioned by their lawyer in TFA.
See for example https://www.popehat.com/2013/09/05/ninth-circuit-clarifies-f...
> First a court must determine whether or not the speech is on a matter of public interest. Speech on matters of public interest are entitled to protection, even when uttered by employees; speech on purely private matters (like, say, a private and internal spat among employees) is not. Then the court must balance the employer's interest in an orderly and efficient workplace against the speech rights of the employee, taking into account things like whether the speech restriction is content-based (that is, whether it censors some viewpoints but not others), the circumstances of the speech, the strength of the employee's interest in the speech, whether the speech genuinely disrupts discipline and order and interferes with relationships, and so on.