The Right To Privacy vs. The Right To Gossip

Warren and Brandeis argue that the protection of privacy is the default until such a reason arises warranting an invasion of this privacy. They characterize vaguely the circumstances whereupon the public may invade the privacy of the few such that the concern must be of the many, and not of few. Matters are private when one has "...not assumed a position which makes their doings legitimate matters of public investigation." He earlier differentiates between publishing the woeful qualities of a retiree versus those of a political candidate as only acceptable in the latter case. In general then they create an exception for cases that serve the interest of the public at large; my question is how large?
It is acceptable to publish everywhere the incredible lack of brains our president wields, and yet if you send out emails to everyone denouncing and warning of a particularly horrid teacher on campus I have no doubt UCSC would move swiftly to expel you on grounds of libel and character unbecoming of a student or something. But don't we all deserve to know about poor educators in order to avoid them? If we are allowed to gossip about the character of a potential political representative, how is that different from the right to know if someone you're interested in is a cheater or has stds or whatever? If you can reason that particular gossip can protect you from potential harm don't you have a right to hear it?