Prior to antibiotics and modern medicine, AIDS would have not been distinguished from pneumonia, blood poisoning or any other common infection. LOTS of people died of pneumonia before antibiotics.
Postings on this thread describe sexual fetishes that induce abrasion and blood exchange. Sure, these would transmit the disease readily, but they do not represent the risk to the mainstream population.
Sex was a taboo subject in conversation in the 1950's and earlier. Even into the fifties, American women sometimes did not learn the "facts of life" until their wedding night. They had no idea what the adult male body looked like when prepared for a woman.
Going back to 1900, there were "sex guides" for married women that described a "proper" way to engage in conception without the indulgence of pleasure. The couple wore garments in bed and bare skin did not make contact, beyond the "essential" parts. Proper people did not French kiss. That practice remained unknown to many adults well into the sixties and later.
There is evidence that AIDS had indeed been around in previous generations; it just was not diagnosed. There was a case of a teenage boy who kept developing infections and eventually died in the mid 1960's. The doctors thought the case was unusual, because conventional medicine at the time should have cured the infections. They froze tissue samples after the patient died. A sample was thawed and tested in the 1990's, and the results indicated AIDS.