A cyber bullying prevention policy is essential in a modern school - and it should protect not just students from one another, but teachers from students and their parents (and vice versa, of course, though almost all teachers will have the professional nous not to engage in anything anyway). It protects people from horrible bullying, and actually it protects young people and children from living with their own horrible choices as teenagers when in their twenties and thirties, too - the internet is not always as transient as kids seem to believe. At that age, they think they are, as another commenter said, Teflon-coated. They should be protected from themselves, as well as one another.
That is very different to a policy aimed at preventing legitimate scrutiny and shutting down any form of potentially valid complaint. The latter is draconian, an abuse of position, and actually not in the public interest.
Those arguing that you can't have the former without the latter seem a tad confused - how do they imagine the rest of society navigates this dilemma? You can't use social media to harass, distress or annoy. You can't make defamatory claims. You can make fair comment, you can offer valid factual evidence, and you can question, challenge, and disagree.
A blanket policy that is framed as though created to protect pupils, but actually used to stifle perfectly reasonable debate and criticism, is an abuse of power.