I suspect it's classed as gross misconduct.
I'd expect the same for teachers. We have a code of conduct we sign and have to adhere to.
Social media is a minefield for school staff. I have mine locked down. I removed any possible drunken looking pics.
We have to uphold the British values, and code of conduct. Deliberately and publicly stating views against this would be gross misconduct.
Imagine "teacher declares minority ethnic communities shouldn't have same rights as whites"
"Teacher states that mixed race marriages aren't normal"
It's the same thing.