If you read about the group backing the teacher you would see that far from promoting “free speech” they are committed to ending free thought and freedom if association as they are strongly opposed to gay rights, fay people, and Transgender people. In the US “free speech” has been used as a fake wedge issue by far right agitators. They begin by bringing law suits supposedly protecting the “free speech” rights of conservatives to (for exampke) preach against gay people, fay marriage, or DEI, or critical race theory or even jjst teaching that the US is a multicultural society and once they win the case they start radically suppressing everyone else’s speech in the name of religion or politics.
Free speech is a tactic in a long war against the rights of women, gays, immigrants, and people of colour. Its not the desired goal of the teacher or his religious supporters.