The only example that stands for your point is HIV, most epidemic and endemic infections that primarily involve homosexuals are from amplification of existing, sometimes even ancient, pathogens.
This article was written to pump up concern about a common, long-understood respiratory virus, presumably to whip people wavering on "following the science" back into line.
HIV/AIDS (1981): Because San Francisco had a highly organized gay community, doctors were able to spot the pattern of falling T-cell counts and rare infections much faster than in places where the population was more isolated.
Mpox (2022): San Francisco was one of the first cities to declare a public health emergency. The community’s proactive response and demand for vaccines actually helped create the blueprint for controlling the virus nationwide.
Shigellosis & Meningitis: Periodically, outbreaks of antibiotic-resistant bacteria or specific strains of meningitis appear in the city. Because the SF Department of Public Health (SFDPH) monitors these groups so closely, San Francisco often issues the first “warning” to the rest of the world.
There are others, but is what was allowed to be searched.