the differing standards for libel & slander

The law has a different standard----a higher one----to prove slander or libel for public officials than for private citizens.   The rationale is based upon the concept of need to promote "the public good".   The laws against libel and slander is to protect ordinary citizens from egregious, 'knowingly-untrue' words or writings against a private citizen.   However, the public at large, the citizens, have the need to be able to freely critique public officials and politicians in their performance, to promote better government, and to promote the free exchange of ideas among the residents.