if i were a teacher, i would be loving terrified of the idea that i might get fired for accidentally letting an opinion slip out. good teachers might, from time to time, show their opinions when it might be a bit inappropriate. if a teacher is constantly talking about politics, that obviously becomes more questionable. a singular instance like this one isn't nearly enough information to say that this teacher should be fired. you're certainly playing with more fire talking about politics as a teacher, because students take the things you say as educational rather than necessarily subjective, but teachers are also human and can make honest misjudgments. i don't think anyone here is actually saying teachers should be fired for expressing opinions in the most broad sense, but i still don't agree with the idea that good teaching is impossible when a teacher states their opinions