When I was a teen, I used to browse used book stores, of which there were many in my city. I remember picking up a book called, IIRC, "The Fifth Man", written by a homosexual male. Predictably, it claimed that 20% of the male population was 'gay'. That was back in the mid-sixties, so this kind of propaganda has been going on for a long time.
I think Kinsey, the homosexual propagandist, claimed an even higher number. His work has been thoroughly discredited, but the myth lives on.