Hilchos Rechilus, chapter 7, section 2

Rechilus applies to speaking about an ignoramus because he counts as a fellow Jew (amecha). This applies even if the ignoramus insulted someone for no reason, for we explained in chapter 1 that rechilus is even about the truth. It is even worse to speak rechilus of a Torah scholar for many reasons. a) Rechilus is worse when it is untrue. Because a Torah scholar generally does not insult or do something against someone for no reason, speaking of him as having done something wrong is false rechilus. b) The Torah commands us to cleave to a Torah scholar in every way, to eat and drink with him, do business with him, marry one’s daughter to him, and accord him much honor. How much may one not entangle him in controversy, which is opposite of all the above. c) A person is less aroused if he hears that an ignoramus insulted him or did something against him. When he hears that a Torah scholar did such a thing, it arouses great hatred and very often leads to controversy. If one speaks rechilus against the rabbi of the town it is even worse and certainly leads to very great evils, sometimes costing him his livelihood.