They represent the state. Their speech cannot be silenced, except when on the job. At least, my opinion is it shouldn’t be.
Otherwise, all government employees would have no first amendment rights. And at the rate we are going regarding the percentage of the country that works for the various branches of government, that would imply that soon no US citizen would have first amendment rights. ;)
You're good with federal judges silencing speech on the job in the name of the 1st Amendment? Orwell lives.