Educating people about HIV and Alzheimer's Disease is understandable since I can tell you things about them that you probably did not know. In the case of HIV, knowledge helps clear the irrational fears (due to ignorance) that often leads to social stigma surrounding the disease. As for Alzheimer's, a lot of people do not have enough knowledge about the disease process and affected individual's perception of reality which often makes their loved ones needlessly frustrated or even angry at the person suffering from AD.
Trachoma is an infection of the eye. I really don't see any reason to tell everyone about it. You might as well take a medical course on different types of diseases and infections while you're at it.
