I am NOT a teacher, but: both my parents - mum has only just retired after 45 years of service at the beginning of the last summer holidays - were.
I am also from a deeply political family!
At "home" (if you still get to say "home" about "where my parents live" when you are 40), we are - and were brought up to be - hotly debating political issues over dinner. There were clear rules that everyone accepted: "no glorification of violence", "no total dehumanisation of the other side", ... if you happen to be reading "clearly, she grew up in a leftist environment", you would be spot on!
Teachers are only human, too! And, generally speaking, they have the same right as everyone else to - outside of their workplace - engage in political activity as everyone else!
Do NOT shut teachers up! They may hold opinions that you like more or like less! DO complain of and when they start to lecture, in the classroom!
EDIT: I am saying this as "I am, currently, a corporate executive - and, now THAT is a job that genuinely forbids me, by contract, from openly stating that I ACTUALLY think a certain national [insert strategic resource] company of a certain country (also, a big "ally", politically speaking) in actual reality gives about 0 fucks and pays my employer very handsomly to "greenwash" on their behalf!