according to Mill's principle, infringement on the freedom of an individual's speech and expression is allowed (in fact, encouraged) when his speech will cause harm to people other than himself.
by this token. if by btching about their teachers on logs, they are harming the teacher's feelings, motivation etc, as well as give the public a bad impression of teachers (and hence undermine their authority), then such blogging should be exterminated.
but of cos this is just philosophical. still.. it sort of makes sense lah....
and that is beside the fact that i will always side with teachers.