What I'm saying is that what we understand as heterosexuality is a spectrum but it is a simplistic one because human sexuality is complex and diverse. Usually people who identify as heterosexual and are mainly heterosexual have had homosexual feelings, attractions, experiences, etc at some point in their lives. So yeah the category works because most people fall on that spectrum but that doesn't mean that a person identifying themselves as heterosexual have been engaged or have had or will have exclusively heterosexual feelings all their lives. I think Kinsey's research as well as further research on sexuality of humans and other close species to ours have made it clear that it is not such a black and white division. That doesn't mean that heterosexual practices are not the norm in humans, which they are.