This is not a freedom of speech issue. Teachers are already free to express their own views during their own free time. When teaching in a school however they are limited by the demands of what is necessary to teach their pupils. Freedom of speech does not give teachers qualified in one subject the wherewithal to teach their class a different subject which is effectively what teaching creationism means. Creationism should remain in religion classes and evolution should remain in science classes. Teachers are employed by the state in order to teach children facts, not spread personal ideology. It is therefore best to seperate facts and ideas into seperate subjects.