It was more than just one gay man, funnily enough I just watched
'And the band played on' (a 1993 movie about the HIV-Aids epidemic) and the number of people who caught HIV via blood transfusions ran into the tens of thousands, most of which the blood came from gay men who had donated blood. It mostly effected haemophiliacs as they require regular blood transfusions, and was essentially a death sentence for no fault of their own. Awful.
You can watch the entire film via YouTube, pretty interesting and based on real people:
https://www.youtube.com/watch?v=4UGLZXEJoyo
A much much much higher risk. If gay sex were the norm throughout western countries, we'd literally have an HIV outbreak on a scale of parts of southern Africa.
I think of all new HIV transmissions today, something like 50% or just over are gay people. That's a hell of a lot considering they're 1% to 5% of the population.