The purpose of pubic relations is to manage the image and perception of a person or a company, for example, by the society, potential clients, partners, etc.
A public-relations speech will help achieve the goal above by providing information that is, for example, beneficial to a company, advertising its qualities and advantages over others. That seems to be the case with the speech mentioned in the question. The representative of the local tour bus company is basically managing the image of the business by advertising its advantages in offering services for the visiting dignitaries.
The Logan family and Mr. Morrison are trying to take a stand against the injustice against blacks by whites that is rapidly building up to a crisis—like the Wallace store boycott, or Mr. Morrison's violent defense of Papa.
