The word heterosexual is an adjective, the word homosexual is an adjective. They describe an activity. Of course there's a homosexual activity; of course there's a heterosexual activity. But there's no homosexual person. There's no heterosexual person. Everybody is everything.
What the Kinseyites and I had in common so long ago was the knowledge that homosexual and heterosexual behavior are natural to all mammals, and that what differs from individual to individual is the balance between these two complementary but not necessarily conflicted drives.